Roberto Martínez has issued a staunch defence of John Stones and claimed the young Everton centre-back has the ability to become one of England’s greatest players.

Stones has attracted criticism at Goodison Park recently and his error against Swansea City on Sunday led to Gylfi Sigurdsson opening the scoring in the visitors’ 2-1 victory. The 21-year-old, denied a move to Chelsea last summer, faces a fight to retain his place in the Capital One Cup semi-final second-leg at Manchester City on Wednesday with the captain, Phil Jagielka, available having been rested for the Swansea defeat.

The former Barnsley player has been a regular feature in an Everton defence that has conceded 22 goals at home in the Premier League this season. No other Premier League has conceded more. But Martínez insists he will always protect the club’s young talents and has backed Stones to overcome his current struggles and develop into one of English football’s finest assets.

Martínez, who recently described Gareth Barry as “one of the best English players ever”, said: “My take is the one I always have with young players. John is 21, he’s played 68 games in the Premier League and I wouldn’t judge or assess it until a player has played 100 games in any division. What I will say is that he has incredible potential, he is still young and in the right environment to develop. Whatever criticism from outside we accept, but John Stones is in the right environment to fulfil his potential as one of the greatest players England has ever seen.

“John is the first to know when he plays bad or well, he doesn’t need telling. You need to feel support and warmth of your club and he has that in huge amounts. He will benefit once more. Is he the finished article? Clearly not because he’s only 21. Psychologically you need to go through those experiences to create a winning mentality. When things go well the young players get a lot of attention and when they are not going well they have to get used to that scrutiny, but I never manage in a blame culture.”

The Everton manager confirmed Muhamed Besic and Kevin Mirallas will miss the Manchester City match with injuries sustained against Swansea but James McCarthy, who has not played this year due to a hip problem, should be available.