Pep Guardiola defended Rico Lewis for his performances this season after the Manchester City defender returned to the England Under-21 squad while Kyle Walker made the seniors. Lewis, who broke through in the Treble season, looked set for new heights as he started the season in outstanding form and was central to the plans of interim England boss Lee Carsley. Guardiola admitted that he played Lewis more than he should have done in the early months of the campaign as injuries plagued the rest of the defence, and the 20-year-old's levels dropped as he struggled to maintain his performance standards. He has been used less frequently in recent months, although the problems in the backline mean that he has still been regularly needed; last Saturday, he came off the bench to replace Matheus Nunes at right-back after the Portugal international picked up an issue in the first half. Lewis' performances have not been enough to earn a place in Thomas Tuchel's first England squad; instead, he is back in the Under-21s with Carsley. Walker, meanwhile, is in the senior group despite giving up the City captaincy in January to move to AC Milan. City manager Guardiola has been tight-lipped about Walker since his loan exit, and did not even refer to him by name on Friday as he defended Lewis for always giving total commitment to being fit. "Since the pre-season, he has been always available with no injuries," he said. "I admire the players that live 24 hours to be fit, to be ready. "And he has done it since the pre-season. And played a lot of minutes, he deserved it. And now, of course, for the absence of our ex-captain here he can have more minutes and give us something really, really good in when to play. "He's so young. People forget how young he is. And it's a big success that he's in the national team with the under-21s. The future of every single player depends on them." Lewis is not the only player who has struggled this season in a City team that have slumped from their usual high standards. Phil Foden told the Manchester Evening News in January how he had been physically and mentally burnt out from the previous season and had struggled to find any rhythm, while other players who have largely avoided injury - Bernardo Silva, Ilkay Gundogan and Ederson - have also faced a battle to keep their levels. Guardiola denied the suggestion that Lewis is low on confidence as he fights for form, instead indicating that Lewis and Foden had been given a helpful reality check after unbelievable success in the early years of their career. "He has always being confident. He's so strong. Rico is so strong," said Guardiola. "When he makes a mistake, he's always present again in the action. So, I don't have any doubts about Rico. "Of course, he has to improve because sometimes we demand something, we want something of him with the age that he has. It gives time to get better. And this is an incredible experience. "He arrived, like Phil arrived, and every time it's Premier League , Premier League, Premier League, Champions League . And we spoke about it. It's a reality of football as well. Now he's living a reality that I've not seen before. "It looks like business is easy - business is tough. And I'm pretty sure it will help him in the future to realise that, wow, it can happen as well to have a bad season, bad moments. But it's how you react to that."