The group - which also includes Dougie Poynter, Danny Jones and Harry Judd - were training with the Saracens rugby squad to promote a concert at the Watford club next month, but one of the players sent Tom flying, much to the initial amusement of his bandmates.
However, they didn't find it so funny when Tom had to be stretchered off and treated by the club's medical team on Wednesday (15.02.12).
He is still in agony and can't play his guitar - putting the their highly-anticipated UK tour in jeopardy.
Tom told the Daily Mirror newspaper: "A guy from the rugby team knocked my shoulder a bit and it is partially dislocated. To be honest, he hardly touched me - which goes to show how massive and strong he is, or how embarrassingly puny I am. Probably a combination of the two.
"I'll be fine... I just can't move properly at the moment!"
Jackson Wray - the player who injured Tom - is hoping he recovers in time for the start of their 42-date tour.
He said: "The McFly boys really got stuck into training. We were all really impressed.
"They took quite a few big hits from some big guys and didn't complain once. They are tough guys.
"I just hope Tom has recovered in time for the band's gigs."