By SABC Sport
26th July 2023
Mullin sustained a punctured lung following a clumsy challenge from goalkeeper Nathan Bishop in their friendly pre-season game against Manchester United in America.
Mullin was able to walk off the field after some lengthy treatment with an oxygen mask around his neck.
Wrexham went on to beat a young United side mainly comprised of Under-21 players 3-1 at a sold-out Snapdragon Stadium in San Diego, but Parkinson was furious with the tackle on Mullin.
He said: "Mulls is in hospital at the moment. He has a small puncture in his lung. I've just had the call and it will be tomorrow morning before the specialist sees him.
"It is a real blow for us, you can't hide away from that. I thought it was a clumsy challenge from the goalkeeper and it should have been a straight red.
"If it is not denying a goalscoring opportunity, it is still a dangerous challenge.
"So, if you add the two scenarios together, he should have been off the pitch. It was a dangerous challenge and Mulls is our talisman.
"I'm fuming with it, I have to be honest about that. It was a clumsy, reckless challenge in a pre-season game. I can't say any more than the fact Im not happy with it at all."
United were reduced to 10 men when Dan Gore was sent off and Elliot Lee, Aaron Hayden and Sam Dalby all scored for Wrexham.
However, the newly-promoted Red Dragons kick off their season in League Two against MK Dons in 10 days and Parkinson admits he does not know how long Mullin will be sidelined for.
"The way the lads responded after that was outstanding. That is what we are all about as a group - resilience and sticking together," he said.
"I don't know what happens next with Mulls. I've only just got the news in the second half. One of the physios went with him to hospital and we will find out later (the extent of the damage). No idea, as yet how long it will be.
"But he's out for the start of the season. If you have a punctured lung and only 10 days to get fit, you have to say that's that."
United coach Travis Binnion also reflected on the incident post-match.
"Obviously, there's a challenge in the first half when Mullin gets injured, we hope he's alright. I know Bish has reached out to him already and the referee could have sent him off for that," Binnion said.
"It's part and parcel of the game, nobody wants to see anyone get injured. He's made an honest challenge, he's come off worse. He's already reached out to him.
"Booing him, it is what it is. He's tried to reach out. He's a great lad Bish, he hasn't got a bad bone in his body."
The PA news agency understands United are unhappy with Parkinson comments about Bishop, feeling he is inflaming the situation unnecessarily.