England star Rooney is fighting for his Old Trafford future with his current contract running out at the end of next season, with no hint so far that United bosses are planning to extend his stay.
Club record scorer Rooney only started 15 times in the Premier League last season, and scored a career low five times as he struggled for minutes.
Everton and a series of Chinese Super League clubs have been keeping tabs on a potential summer move.
But Rooney has gone all out to prove his fitness to United boss Mourinho this summer by taking part in a brutal spin class.
Liverpool based gym Rise Cycling tweeted a picture of Rooney looked red faced followed a session to get him fighting fit for the new campaign.
It isn’t the first time the former Everton goal machine has been hitting the gym this summer to show off his fitness.
Last week Rooney was caught going through the paces on a treadmill while on holiday in Ibiza.
A fellow guest at his hotel videoed him and said: “Wayne has been going in the gym two or three times a day to work out.
“He has made a big effort to be in top condition and it looks as though it is working.”