An angry Phil Parkinson warned Nathan Bishop to “stay away from Wrexham” after the Manchester United goalkeeper’s challenge on Paul Mullin that punctured his lung and will rule the striker out of the start of the season.

United are understood to be unhappy at the Wrexham manager’s comments, as the club believe they have inflamed what it views as a non-malicious act and could potentially drive abuse via social media at the 23-year-old. Bishop has tried to reach out to Mullin and his team-mates.

The incident occurred 12 minutes into Wrexham’s 3-1 preseason win over United at San Diego’s Snapdragon Stadium. Mullin required an oxygen mask and left the field following seven minutes of treatment. Bishop was booked for the challenge.

Parkinson said: “I’m fuming about it, I’ve got to be honest with you. 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.

“It’s a clumsy challenge from the goalkeeper, I’m disappointed with that. 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 scored 47 goals last season and his loss is a sizeable blow ahead of Wrexham’s League Two campaign, which begins next Saturday against MK Dons.

“It’s a dangerous challenge and obviously Paul Mullin is our talisman,” said the manager. “The way the lads responded after that I thought was outstanding. That’s what we’re all about as a group - resilience, sticking together. And that’s what we showed.

“We’ve only just come off the pitch. We’ll assess things tonight, find out the extent of the injury and then make decisions accordingly. We’ve got options but we can’t hide away from it. Mulls is an outstanding player.

“We just got a call from the hospital to say there’s a small puncture in his lung. It’ll probably be tomorrow morning before we get the specialist to have a look at it.”

Bishop was part of a United team that contained junior players apart from the 35-year-old Johnny Evans.

Travis Binion, the manager, 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.”