Jack Grealish said his omission from England's Euro 2024 squad was "the most difficult thing I've ever had to deal with".
Grealish was left out by Gareth Southgate, despite having been a regular in England's set-up since 2021.
The playmaker, who joined City from Aston Villa for £100million after helping England reach the final of Euro 2020, endured a stop-start campaign for Pep Guardiola's team in 2023-24.
Grealish scored three goals and set up a further three in 36 appearances in all competitions for City last season, but injuries and a loss of form meant he often had to settle for a cameo role.
But after missing out on Euro 2024, the 28-year-old has additional motivation to get back to his best.
"I'll be honest it was probably, football-wise, the most difficult thing I've ever had to deal with in my career," Grealish said ahead of City's pre-season clash with Barcelona.
"I was absolutely heartbroken and then obviously when you're on your holidays, wherever I was, every time you turn on the phone or turn on the TV or whatever, you just see it. So it was hard to not to see it.
"For myself now, moving forward, I have to just try to use that as motivation going into this season and try to have the same mentality as I had two years ago.
"In my first season at City I don't think I performed as well as I could and in the second season I played in a lot of the games and that was down to the first season. I had wanted to come back stronger and I certainly did that, so hopefully I can do that again.
"This is my chance to get my fitness, to have a two-week head start and try to be as fit as possible. And I'm playing with confidence. I feel like that's what I need and fingers crossed I can do that."
In Guardiola, however, Grealish feels he has the ideal mentor.
He added: "I always speak to him. I won't go into too much detail about what we speak about because that's between me and him.
"He's been so good for me in the three years I've been here - there’s not too many people better to take advice from. Pep is a master in this game."