Grennan scored for England as they lost on penalties to the World XI at the London Stadium.
The pop star received the Man of the Match award, though, and his footballing talent surprised many.
He left the match on crutches, but didn't have too many hard feelings towards the Frenchman.
"I've left with torn ligaments in my ankle," he told talkSPORT Breakfast. "Patrice Evra went absolutely through me.
"I've been doing festivals with a boot on and I've got to be in it for six weeks, which isn't great!
"As a United fan, not many people can say Patrice Evra has absolutely clamped you.
"I got a nice message off him and he's sound."
His talents on the pitch shouldn't be a huge surprise though as the 27-year-old had a scholarship offer to go and play football in college in America, but turned it down and pursued music.
He is keen to play more football now and made a plea for non-league managers to get in touch.
Grennan added: "I play 9-a-side on a Thursday. I don't have much time, but if anyone is listening to this and has a non-league football team that is close to the London/Hertfordshire area then hit me up because I really do want to play a bit of non-league.
"When I played in Soccer Aid, I still had the legs for it. When you are in a changing room the banter is unreal.
"I'd love to get back and do a bit of football. My time is very limited, so I'd have to be in and out."
Grennan has a busy summer of festivals lined-up, but he also has a very important engagement this weekend.
And as he is a huge Manchester United fan, it will be even more special.
"I'm actually going to the south of France this weekend, I'm playing someone's wedding," he said.
"It's Harry Maguire's wedding, which I am buzzing about. I'm doing big Harry's wedding, then I get back and I'm going to Silverstone.
"Then Kendall Calling, Boardmasters, but unfortunately not doing Glastonbury… they are still sleeping on me. Hopefully next year!"