The England boss came under fire after the Three Lions did not win any of their four matches in the tournament in June but Grealish feels that the manager's achievements with the national team should be taken into account.
The Manchester City player said: "I think it was harsh.
"We reached the final last year and then the Hungary game (we lost 1-0) at the start of the last camp, I think before that the last time we’d lost a game over 90 minutes was maybe Belgium in November 2020 or something.
"So, I think it is very harsh, especially (as you saw at) the World Cup and the Euros of how well the team done and the manager himself."
England face relegation from the top tier of the Nations League if they lose to Italy on Friday (23.09.22) and Grealish confirmed that the games will be used as preparation for the World Cup.
He said: "I think for us, it’s something we’re obviously aware of, but something that we’re all embracing.
"Especially, I’m not going to speak for the manager, but I’m sure he’s got certain players that are 100 per cent to go to the World Cup, and then there’s obviously certain places and numbers that are still up for grabs. We’re just all training as normal.
"We have two matches now that are going to be very tough opposition and this is really like your pre-World Cup camp."
Grealish continued: "We were saying before that before the Euros we had a good few weeks of training sessions, good friendlies, and we’re not going to get that this time.
"But everyone’s in the same boat, so it’s something that we need to embrace and look forward to."