Wrexham striker Paul Mullin suffered a punctured lung during a 3-1 pre-season win over Manchester United on Tuesday, when he collided with the opposition goalkeeper in the pre-season friendly in San Diego, California, manager Phil Parkinson said.
Mullin, who was Wrexham's leading scorer last season with 46 goals in all competitions, collided with United's Nathan Bishop when the goalkeeper rushed out to stop a long ball.
Mullin stayed down and was attended to by physios who gave him oxygen while a stretcher was also brought out. However, the 28-year-old was able to walk off the pitch before he was replaced.
Parkinson said he was left "fuming" after the goalkeeper received only a yellow card for the challenge and revealed Mullin had been shifted to the hospital.
"It was a clumsy, reckless, challenge in a pre-season game and I'm not happy with it at all. I haven't seen the goalie and he's probably best steering clear of us for the time being because we're not very happy," he said after the game.
"It should have been a straight red. If it's not denying a goal scoring opportunity it's still a dangerous challenge. So if you add the two scenarios together he should have been off the pitch."
Mullin later posted a message on Instagram saying: "Thank you for all your messages! All good here!" with a thumbs-up emoji.
Bishop later posted an apology on social media, wishing Mullin the "speediest recovery".
"(It was) a complete misjudgement and a genuine accident with zero malicious intent at all," he said.
Wrexham's owner, the Hollywood actor Ryan Reynolds, took to messaging platform X, formerly known as Twitter, to wish Mullin a speedy recovery.
"Paul Mullin puts his last drop of blood into everything he does. The entire Wrexham AFC community is pulling for a speedy recovery," Reynolds said in a post.
Elliott Lee, Aaron Hayden and Sam Dalby scored for Wrexham while Marc Jurado scored for United, who fielded a second-string side filled with youngsters.
Wrexham gained worldwide recognition last season when the Welsh club - taken over by Reynolds and fellow actor Rob McElhenney in 2020 - secured a fairytale return to the English Football League after a 15-year absence.
The club's rise in popularity has seen them play pre-season friendlies with top-flight Premier League teams this month. They played Chelsea last week but lost 5-0.
Wrexham begin their League Two campaign at home against MK Dons on August 5.