The defender made a brief debut as a 17-year-old in Europe in 2014 but has had a long wait to return and is aiming to make up for lost time against Fiorentina on Thursday

On 30 March 2014 Leah Williamson, one day after her 17th birthday, made her debut for Arsenal. It was a tough ride. She had been chucked on for Rachel Yankey in the 81st minute with the team losing 2-0 to Birmingham in their Champions League quarter-final second leg and about to crash out 3-0 on aggregate.

Fast forward five and a half years and Williamson, one of the league’s best centre-backs and decorated with every domestic trophy available, is preparing to compete again for “the one”, as Arsenal make their Champions League return against Fiorentina in the last 32.

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“It’s always the one,” she says before Thursday’s first leg in Italy. “I was a mascot for the final in 2006 [when Arsenal completed a historic quadruple]. I know how amazing that was to be in a packed Borehamwood, to beat the best side in Europe at the time and to be with the winning team.”

The nine minutes that kickstarted her Arsenal career may have seemed insignificant, beyond sating a desperation to make her senior bow, but looking back they were hugely influential. “That experience has been quite important to me. I’ve been involved at Arsenal for ever; me and my mum used to do the turnstiles, so I was at every game. I knew what was going on, I knew the feel of the team, but to actually be involved? And to be with people like Rachel Yankey, who was so disappointed because Arsenal should have never been losing that tie? You just felt: ‘This can never happen again.’”

With Arsenal unseeded, they could have faced any of Europe’s giants, and Williamson was convinced they would draw the holders, Lyon. “I was slightly relieved, obviously, to avoid the top. But at the same time I was thinking: ‘They don’t want to draw us either.’ For a non-seeded side we’re pretty good.”

Fiorentina, though, will be no pushovers. The Serie A runners-up have reached the last 16 in the past two seasons and have been labelled the favourites by Arsenal’s manager, Joe Montemurro, “because they’ve been in the Champions League and they know what it’s like. They’ve got a very good team”.

Montemurro, who believes it is time for a group stage and for teams to be added to the competition, steered Arsenal back into Europe after 18 months in charge, much sooner than he and the club had planned for.

“His management style is to set a base, almost a set of rules, and to follow them,” Williamson says. “And then the rest is you. It’s almost like writing a paragraph and you adding in your own notes on the side. The freedom that he gives everybody – he just wants you to be the best player you can be and the best person.

Facebook Twitter Pinterest Joe Montemurro watches training at London Colney this week. The Arsenal manager believes Fiorentina are favourites for the knockout phase Champions League tie. Photograph: David Price/Arsenal FC via Getty Images

“We spend two hours on the pitch a day, if that. The rest of it is about you as a person. It’s human interaction. He is a human. I like him and I trust him because I respect him as a human … It’s almost like the football is a byproduct of everything else.”

The manager echoes his defender’s analysis. “I coach because I love football,” he says. “But the most important thing for me is that these players all walk away with a life skill, with a love for the game, with a love for humanity, with a love for who they are … When they learn about life, learn about respect, when they learn about being able to rely on each other, these life skills are for me the most important thing.”

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Last season Arsenal’s squad was pushed to its limits by an injury crisis that led to seven players being sidelined for significant periods. “There was such a focus on just trying to stay healthy, because we were dropping like flies,” Williamson says. They have strengthened but the squad remains compact and, although Champions League games have been added to the schedule, Montemurro is happy to take that risk.

“I don’t like working with 24-25 players, when player 22 knows that someone has to get injured to even get on the bench,” he says. “That’s not fair to someone. We’ve only got really 20 players. We’ve lost Dan Carter, today it looks like Tabea Kemme is going to be out for a while, so really we’re down to 18 players.

“I think continuity is important. Rotation, I think, is a bit of a false thing. I want everyone to feel that they’ve got an opportunity, that they’re close, that they are one training session away from being in there. That keeps the stimulus high, the level high and the attitude high.”