Manchester City forward Erling Haaland has been experiencing muscle discomfort, manager Pep Guardiola said, after the Norwegian was substituted at half-time for the second straight match on their preseason tour of the United States.

City were beaten 4-1 on penalties by Barcelona after a 2-2 draw in Florida. Haaland was also replaced at half-time in their 3-2 loss to AC Milan in New York at the weekend.

"He's got some niggles. He didn't feel good," Guardiola said on Tuesday. "[It is] disturbing something, he doesn't feel comfortable.

"Muscular niggles is not worth the risk. Sooner or later he has to take a step. To lose him for three weeks, that would be a problem as 60-70% of the squad are on holiday."

Premier League champions City play FA Cup winners Manchester United in the Community Shield on Aug. 10 before beginning their League title defence with a trip to Stamford Bridge to face Chelsea on Aug. 18.

Meanwhile, Jack Grealish has opened up about his omission from England's squad for the European Championship and said he was "heartbroken" after being left out of Gareth Southgate's squad.

"When you are on your holidays, every time you turn on the phone or the TV you just see it [the tournament], so it was hard not to see," Grealish said.

"I'll be honest, football-wise it was the most difficult thing I've ever had to deal with in terms of my own career.

"I was absolutely heartbroken. For myself now moving forward, I have to just try and use that as motivation going into this season. I felt I should have been in the [England] squad.

"I feel like I offer something different to players in the England squad. But it is what it is.

"As I said, it was the hardest moment for me as a footballer. I've had a lot of ups and downs in my career."