Guardiola believes the Serbia international's return to Rome was the best decision for all parties.
"Kola helped me a lot last season in terms of many, many things," Guardiola said after his team's 2-0 pre-season loss to Manchester United.
"But he had a big chance to go back to Rome where he was before and he spoke to me, the club and asked me to leave.
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"I don't like to stay with players who don't want to stay. That's why it's the best option for everybody.
"I wish him all the best because he's a really nice guy. We had an excellent relationship. I was very pleased to train him and I wish him and his family the best."
City are short of defensive options after releasing Pablo Zabaleta, Gael Clichy and Bacary Sagna in May and failing to find adequate reinforcements, forcing Guardiola to use midfielder Fernandinho as a full-back during Thursday's game.
"We don't have another option, we don't have full-backs," Guardiola told the post-match news conference.
"We try to buy full-backs on the right side, not just Kyle (Walker) because the other three full-backs we didn't extend the contracts.
"Kolarov is one step to go to Roma. That's why we don't have any other options."
City will continue their International Champions Cup run against Spanish champions Real Madrid on July 26.
(Reporting by Aditi Prakash in Bengaluru; editing by Amlan Chakraborty)
