British discus thrower Lawrence Okoye has made his NFL debut for the San Francisco 49ers but says he is still "just a bad football player"

Lawrence Okoye is not good at his new job. Less than one month away from the start of the NFL season, the San Francisco 49ers' rookie defensive lineman has poor technique, minimal experience and only a modest grasp of the game's strategic element. And that is exactly where he was hoping to be.

"My goal with my coach, the first step was to get to a position where I could be looked upon as just a really bad football player," Okoye told local reporters on 7 August. "A really bad guy. Just a bad football player. And I think we're getting to that stage."

Catching up with Okoye a few days later at the 49ers' practice facility in Santa Clara, I ask the former Olympic athlete to explain what he meant.

"Well the first step towards being a good football player is to be a bad football player. Right now that's what I am. The next step is for me to work hard and see if I can become a good one."

Coaches in San Francisco had spent the previous four months trying to work out whether Okoye was capable of becoming a football player at all. He could not be defined as such back in April, when they signed him as an undrafted free agent. Back then he was just a curiosity, the British Olympic discus thrower who woke up one morning determined to prove himself in a sport he had never tried.

Okoye dazzled scouts with his athleticism, running the 40-yard dash in 4.78 seconds at a regional scouting combine, while weighing in at more than 300lbs. He stood more than 6ft 5ins tall and blasted out 30 reps with a 225lb bar on the bench press. The NFL.com analyst Gil Brandt, formerly vice-president of player personnel for the Dallas Cowboys, described it as a "real, first-class show".

But none of it made Okoye a football player. The 49ers had identified him as a defensive line prospect, yet he needed to learn the fundamentals of the game before worrying about the specifics of any particular role. His position coach, Jim Tomsula, likened the experience to working with a new pee-wee football player.

Okoye persevered. Three months later, he took part in his first preseason game; unlike those pee-wee kids playing to a crowd of friends and family, Okoye made his bow in front of tens of thousands of fans at San Francisco's Candlestick Park.

"It was a crazy experience," Okoye tells me, less than 72 hours on from that debut. "Candlestick Park is an incredible venue, with great fans, so to be out there playing my first game a year after taking part in the Olympics was pretty amazing."

He does not seem all that amazed. Okoye's voice does not rise as he recounts his achievements, and nor do his eyes light up. He has achieved more over the past 12 months than most athletes do in their lifetimes – reaching an Olympic final and playing in an NFL game (even if only an exhibition). Not bad for a man who also has a deferred offer of a place to study law at Oxford University.

Reminded of the outlandish nature of his achievements, Okoye responds with a shrug.

"To be honest I don't really think about it too much. I just try to focus about what I'm doing right now and what I have to do next to get better. I try to keep my mind on things that I can control."

Okoye cannot yet control opponents in the way he would like to do. He was on the field for a total of six defensive plays against the Broncos, and only four that were contested as the game ended with two kneel-down calls. Okoye had lined up against some of the Broncos' own fringe players – back-up offensive linemen fighting to make the squad but failed to make any great impact.

That does not come as any great surprise. Okoye had been taking part in full contact practice for less than two weeks, putting on his pads and helmet for the first time on 28 July. The 49ers' head coach, Jim Harbaugh, was impressed just to see Okoye dress himself correctly. "I remember my first padded practice," said Harbaugh. "Pee Wee football, Ann Arbor, Michigan, 1973 … I put the thigh pads in wrong. I had the top part sticking down and the narrow part sticking up."

Lawrence Okoye at the London 2012 Olympics. Photograph: Adrian Dennis/AFP/Getty Images

In the weights room, Okoye has few peers. He claims to be the strongest man on the team, yet is the first to admit that he does not yet know how to use such power to his advantage. A former rugby player with London Irish and Wasps, he relished the opportunity to get back to playing in a full-contact sport, but was unprepared for the different challenges that football would present.

"I go up against two All-Pros every day in [49ers offensive linemen] Mike Iupati and Joe Staley, so I'm working with some of the most talented guys in the league. But Mike also weighs nearly 350lbs. It's been a new experience for me giving up weight to somebody in a physical confrontation. It's not something that ever used to happen for me playing rugby."

Football is different in other ways, too. "In rugby you always need to protect your head because you haven't got a helmet," explains Tomsula. "When you go in for a tackle, you duck your head away to the side. We don't want players to use the helmet as a weapon in football, but it is a protective device. We want our players to always keep their heads up, see what they're hitting and kiss the football when making a tackle."

It is a fine line to tread. Linemen, and especially tall ones like Okoye, must work hard to stay low and gain leverage on their opponents. But as Tomsula points out, a human's first instinct when told to get down is to dip their head. That, on a football field, can be extremely dangerous. Some of the most serious injuries in the sport occur when a player initiates contact with the crown of their skull.

Tomsula has worked hard with Okoye on body positioning. The player has spent significant time in the "coop", a 4ft high metal frame with a mesh ceiling that prevents him from standing up straight, forcing him to bend his knees while practicing different movements.

In the build-up to the Broncos game, Tomsula made Okoye take on blockers inside this contraption. "We had him in there doing one-on-ones, with players going in and blasting him," says Tomsula. "We did that 25 times in a row.

"If you're in that coop and someone fires at you, you better do things right or you can't get out. So we got him good and tired, and looked to see: 'does he still keep bending his knees?' 'Does he still keep his eyes up?' And he did. If he wouldn't have, then he wouldn't have been in for as many plays [against the Broncos] as he was."

It is still very much a work in progress. Okoye stood up far too straight while playing against the Broncos and on the day that I visit continues to make the same mistake in practice. He dismisses the suggestion that this is the biggest weakness in his game, stating humbly that he needs to get better at "everything", yet it is certainly one of the easiest to identify.

Okoye could not hope for a better setting at this stage of his development. Tomsula is uniquely well-positioned to help him develop, having coached for nine years in NFL Europe – where he worked often with inexperienced athletes still learning the nuances of the game.

But that does not mean that we can expect to see Okoye in a regular season game any time soon. It might never happen at all. "I'm not worried about that. I'm just working on getting better every day," says the player when asked about his hopes for the coming year, but he must know that the odds of him making San Francisco's 53-man roster are slim in the extreme.

Winning a spot on the 49ers' practice squad – the eight-man group permitted to train with the team but not to play in games – is a more realistic goal, but even that is no foregone conclusion.

"Lawrence is doing great, he really is," says Tomsula. "But what's our expectation? Is he going to start for us or be in the Pro Bowl this year? No guys, I mean, no. We don't have any expectations that way … He's an athletic specimen, but this game is different to anything else. There's nothing like this game.

"He's got a world to go. A world to go. I don't want to put any undue expectations on where he's headed. The questions I ask every day are: 'is he showing up?' 'Is he working his tail off?' 'Does he want to succeed?' And 'is he determined?' The answer to all of those is yes, so now you've got a tremendous athlete who has got all the intangibles. Let's see where it goes."

For now, Okoye is going nowhere at all. In his estimation, the working day at training camp runs from 7.30am all the way through to 10 at night – encompassing, team meetings, walk-throughs, practice, weight-room sessions and playbook study.

"I haven't seen San Francisco to be honest. I flew out here when they signed me as a free agent and I've been working every day since."

He has struck up a bond with fellow Brit Menelik Watson, the offensive tackle selected by the nearby Oakland Raiders in the second round of this year's draft. The pair met on a flight out to the Bay Area and have stayed in touch since.

"I exchange texts with Menelik. He's another guy who is relatively inexperienced in the sport, so it's great to see how well he's doing. You have to respect how hard he's worked to get there."

Okoye is determined to do the same.

"I was a bad discus thrower once. I don't remember the first time I tried to throw it, but I was about 12 … It didn't go well."

Time is no longer on his side like it was back then. Okoye spent the best part of a decade honing his discus-throwing skills, but has just a few weeks to convince the 49ers that he is worthy of further investment. The 49ers must cut their roster down to 53 players by 31 August, before naming their practice squad a day later.

The chances are that he will still be a bad football player by the time those dates roll around. What Okoye must do is convince his coaches that he is capable of becoming a better one.