Hart spent last season on loan with West Ham after falling out of favour under Pep Guardiola at the Etihad, having spent the previous campaign with Torino in Serie A. 'He's so young and in two years it is another European Championships and then in four years another World Cup.
Guardiola's title-winning squad had 16 players at the tournament in Russian Federation, including England's John Stones and Raheem Sterling, Spain's David Silva, Brazil's Ederson and Gabriel Jesus among others.
Guardiola quickly froze the England global out of his plans after arriving at the Etihad Stadium, handing him just one appearance in a Champions League clash with Steaua in August 2016.
Ireland under-19 global Tyreke Wilson has been called into the Manchester City squad for their pre-season tour of the US.
There is less than three weeks to the English transfer deadline on 9 August - although players can move overseas up to 31 August. He last played a full Premier League season back in 2015/16, starting 35 games for Manchester City.
"I know it's not easy for him". If they want to come, that's great but if he wants to go to Chelsea, all the best for him.
"We tried but my advice always is that players should go where they want".
"It would have been a mistake for him if he came and he wanted to go to Chelsea with (new manager) Maurizio Sarri".
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Promising youngsters Phil Foden and Brahim Diaz are amongst the huge number of academy players in Guardiola's squad.
Manchester City are now in Chicago, Illinois where they have commenced the US portion of their 2018-19 preseason training activities.
"It is what it is", Guardiola told reporters.
"I respect the decisions of the manager, Jogi has the right decisions and there is nothing to say. that's happened, that's why I never did it in the past - make comments about my colleague's decisions".
"We spoke - they have to come back ready", he added. "We have young players who can play, we'll see, Douglas Luiz, Claudio Gomes so we'll see".
City face a Dortmund side that will include Mario Gotze, who scored Germany's winning goal in the 2014 World Cup final. Coverage begins on Sky Sports Premier League at 4pm.
Gotze said: "Every player wants to be part of the World Cup". All the best for him.