Wayne Rooney appears to be knocked unconscious by Stoke City's Phil Bardsley in a video of the pair boxing which emerged on Sunday.
ootage obtained by The Sun shows the former team-mates sparring with one another inside Rooney's house.
Bardsley and Rooney trade blows for a minute in the video, before the Stoke defender lands a stiff left-handed punch on Rooney which floors the England captain.
Rooney falls to the ground with a thud and lies motionless beneath a chair as the video cuts out.
The club refused to comment on the video when contacted on Sunday morning and Rooney's representative did not return calls.
Former Birmingham and Sheffield United midfielder Curtis Woodhouse - who swapped football for boxing and became the British super-lightweight champion - saw the funny side of the incident, posting on Twitter beside two pictures of himself boxing and playing football: "Some can, some think they can #Rooney... not everybody can do it!!! it's not as easy as I made it look."
When asked by one Twitter user whether he would consider fighting Rooney for charity, Woodhouse replied: "when he wakes up maybe"
Rooney in his kitchen, where his Bardsley-boxing appeared to take place (FACEBOOK)
United manager Louis Van Gaal Rooney that he expected pristine off-the-pitch conduct when he made him captain last year. “I like his attitude, of course, on the pitch and on the training ground, and not so outside of the pitch," Van Gaal said.
"But I have explained to him outside the pitch is also very important for me. And he accepted the responsibility.”
The Manchester United captain trained as boxer in his youth, and has frequently socialised with boxers, including Amir Khan, Lennox Lewis and Ricky Hatton.
Rooney is expected to captain United on Sunday against Totenham, and will be accompanied onto the pitch by his eldest son Kai, who is mascot.
"Big game tomorrow against Tottenham at Old Trafford," said Rooney on Instagram. "Looking forward to walking out again with my son Kai as mascot!" the 29-year-old United captain wrote next to a picture of him and his two sons on the pitch before the Slovenia match.
Last November Kai and his younger brother Klay were mascots when their father won his 100th England cap against Slovenia at Wembley. Rooney scored the opening goal in a 3-1 win that night and United will be hoping for a similar result when they face their rivals for Champions League qualification on Sunday.