Roberto Martínez has claimed John Stones has improved on and off the pitch since Chelsea tried to buy the England international last summer and that Everton’s refusal to sell contributed to the development.

Stones faces Guus Hiddink’s side on Saturday having been denied a transfer to Stamford Bridge at the start of the season when Everton rejected bids rising above £30m for the defender. The 21-year-old responded impressively and professionally to the decision, with his performances in a defence hit by injury justifying the stance and attracting links with Barcelona.

Everton’s manager believes a regular starting role at Goodison Park, combined with Stones’s reaction to the pressure of Chelsea’s very public pursuit, has been beneficial. “I think he is better by looking at the amount of games he has played in the Premier League and the amount of starts he’s had,” said Martínez, who hopes to add Leeds United’s Sam Byram to his defensive options next week after an initial £3.7m deal was agreed. West Ham United and Newcastle United are also keen on the 22-year-old.

“It is not just the way he is developing as a defender but the way he is developing as a leader. He is someone who can affect the players around him. His contribution has been magnificent and the way he has had to cope with many aspects that had nothing to do with football is part of his development. Clearly, he is a footballer who is completely different to the one that we had last year and the next 17 games in the league will be pivotal for his development.

“Everything that went on in the summer helped him grow as a person and a player. You need to understand that the human side of a footballer gets heavily tested in that period. You get a lot of influences, some influences were wrong from the outside, and they affect you. Psychologically, he has become a man in a very short period of time and a footballer who knows how to cope with high-pressure situations and being able to perform on the pitch.

“What John has done is always be there to perform for Everton, always be there to help his team-mates and has always made himself available. That is what you want but in modern football you don’t always see that too often in young players.”

Martínez had suggested Stones would be rewarded with a new contract that financially reflected his status as one of Europe’s finest young defenders after last summer’s transfer window closed. However, no deal has been signed. The England international was secured to a new five-year contract in 2014.

“He is still on a long-term contract and nothing has been changed,” said Martínez. “We are treating every individual in the same manner and after January it will be time to look at the individual situations and individual contracts. At the moment, the focus is finishing this window with a stronger squad than we had at the beginning. A couple of players need to be allowed to go out and then after January we will look at things.”

One of those players is Aiden McGeady, who has had loan offers from Leeds, Sheffield Wednesday and Blackburn Rovers but is reluctant to move to the Championship. West Bromwich Albion had expressed tentative interest and the Republic of Ireland international may wait to see whether a Premier League offer materialises before the transfer deadline. Everton have agreed an £8.5m fee with Norwich City for Steven Naismith but the Scotland international, currently out with an ankle injury, is also considering his options.