By NATE ATKINS -- natkins@mlive.com

The NFL has no formula to follow when the blindside protector for a franchise quarterback goes down in June. But when a torn labrum knocked 2016 first-round pick Taylor Decker out for four to six months earlier this month, the Detroit Lions didn't wait around. They explored their own options at tackle and guard, signed players and even made a trade.

The result is a large room of candidates to fill in until Decker can return, likely in the second half of the season. It's a competition that will demand heavy focus in training camp, which starts July 31 in Allen Park.

Here are the candidates the Lions currently have lined up for the job, from the favorites down to the backups and emergency options:

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Greg Robinson

He was the No. 2 pick of the 2014 draft, a mountain of a man at 6 feet 5 inches and 332 pounds who was supposed to be a mauler in the running game as well as a blind side protector. For as bad as Robinson's stint was with the Rams -- when he was bumped inside, benched and traded for a sixth-round pick before he finished his rookie deal -- he still has a ton of potential to offer and might be heading to a pass-blocking system that can better use his quickness and size.

He's the most talented option the Lions could play in Decker's absence. The job will be his if he can show that, but based on his pro career so far, that's everything but a guarantee.

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Cyrus Kouandjio

Kouandjio was another high pick in the 2014 draft, taken in the second round by the Buffalo Bills. He's struggled through injuries each season and has only started seven games. Add in the offseason issues that include a fall at his home resulting in hip surgery and a strange, pant-less incident in a field, and he comes to Detroit with some risk.

He entered the league as a 6-foot-7-inch, 322-pounder with strength and bully tactics in the running game, but the rawness of his technique has yet to disappear. He's yet another talented player the Lions are kicking the tires on as they're unsure they want to roll with backup-type players for an extended period of time.

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Cornelius Lucas

As the Lions are kicking the tires on talented but underwhelming outsiders and trying to get them acclimated to their system, something is to be said for players already trained in the scheme. That includes Lucas, a 6-foot-9-inch, 330-pounder with a track record of working his way up. He joined the Lions in 2014 under Martin Mayhew, and he's stuck with a regime change. That isn't easy for an undrafted player.

With six starts in 35 career games, his job is to patch things together, and the Lions trusted him to do that in a road wildcard playoff game against the Seahawks after Riley Reiff went down last season. The question will be whether they believe in him to do it for four to six months, a timeframe that often exposes backups as such.

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Corey Robinson

Like Lucas, Robinson has established himself as a backup in the Lions system, logging two years since he was a seventh-round pick and playing in 14 games last season. Unlike Lucas, he's not at full strength to jump into a competition like this. Robinson missed OTAs and minicamp recovering from the foot injury that ended last season. When he rebounds, he'll more than likely serve as Rick Wagner's top backup on the right side, the spot he played last year and has the experience in.

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Joe Dahl

One of the Lions' reactions immediately following Decker's injury was to try Joe Dahl out at left tackle. The second-year pro was figuring to factor into the three-way left-guard battle this spring, but Cooter liked his versatility from his Washington State days enough to try the fifth-round pick at the most important spot on the line.

Perhaps the additions of Kouandjio and Robinson say something about what Cooter observed of Dahl in practice, as the experiment figures to be short-lived. At 6 feet 4 inches and 305 pounds with 33 1/8-inch arms, Dahl always projected better as a guard. It's one thing to fill in but another to hold the job for months on end. Consider Dahl more of an emergency fill-in.

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Tony Hills

Hills was the first addition the Lions made at tackle after Decker tore his labrum. Even then, it looked like a depth signing. Hills, 32, is entering his 10th year in the league and has played 33 games with just one start in tenures with five different organizations. The 6-foot-5-inch, 304-pounder keeps finding jobs, but with Robinson and Kouandjio now added to the position and Decker still slated to come back this season, he should be considered firmly on the roster bubble entering training camp.

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Rick Wagner

The newcomer is the Lions' highest-paid offensive tackle and also their most talented, but all indications are that he's not going to play on the left side. He struggled there in his moments in Baltimore, finding the right side to be where he wanted to make his money. He settled for the Lions' offer at the very start of free agency for a reason: He knows what he is and isn't. He's a right tackle and is likely to stay put there despite the needs on the left.

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Taylor Decker, the tackle in waiting

As Matthew Stafford said, it's not like Decker died. He's just going to miss some time. The 6-foot-7-inch, 311-pounder was one of the better run blockers up front as a rookie, improved his pass protection as the year went on and crashed the Pro Football Writers of America All-Rookie Team by the end of it. His quick rise is what had the Lions not focusing as much on the depth behind him, sending them into the tailspin they're in now.

Decker is just 23 years old and played every single snap as a rookie. He and the Lions will hope this ends up being just a blip on a long career at the positions.