The video, obtained by The Sun on Sunday, is said to have been filmed last month and shows the two Premier League players sparring.
Former United full-back Bardsley, who now plays for Stoke City, then connects with Rooney, sending him to the ground.
However, although Rooney is left flat on his back, he appears to brace himself for impact before hitting the floor.
The bout did not seem to do too much damage as, six days after it was apparently flimed, Rooney scored twice in United's 2-0 win over Bardsley's former club Sunderland at Old Trafford.
Rooney is a boxing fan and regularly comments via social media on fights, most recently involving the likes of Paul Smith and Martin Murray.
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