'For the guy, it would have been a mistake for him and for us if he had made a decision to come here when he wanted to go with Maurizio (Sarri) and Chelsea.
"I did what I did in the previous two seasons because I needed to play to be involved in the World Cup", said Hart. We tried but my advice always is that players should go where they want.
"In some minutes we started good and after we had a few problems".
The Algeria star showed glimpses of his quality for the Premier League champions and he nearly scored before half-time via a set-piece but undermanned City fell to Dortmund at Soldier Field.
"Joe is our player, we will try and find solution", Guardiola said.
The 31-year-old has yet to play a Premier League match under Guardiola, and has spent time on loan at Torino and West Ham during the Spaniard's tenure.
So far the tentative interest in Hart - who has 75 England caps, but was left out of the World Cup squad - has come from overseas clubs.
Sane vowed to return stronger following Joachim Low's decision not to take him to Russian Federation, admitting his disappointment at not being included in the 23-man squad, who were eliminated at the group stages.
Sterling had a fantastic season with City, and saw his potential asking price rise in the World Cup in Russian Federation.
City's first league game will be against Arsenal at the Emirates Stadium on August 12 and the Algerian expects a tough game against a new look Arsenal side.
"I really hope that it is a good fit for the game over here and I will certainly be doing everything I can to make sure it works out". "We're looking to decide if he's going to stay or leave, we will see at the end of preseason".