Sky Sports News understands that his assistant Michael Carrick will be appointed temporary manager to the end of the season.
Mourinho's future has been the subject of intense scrutiny this season - and the club's worst start to a season in 28 years was confirmed with defeat at Liverpool on Sunday.
Mourinho's final game in charge was a 3-1 defeat to rivals Liverpool. The 55-year-old Portuguese insisted at Anfield that he had not lost the dressing room, as his team sat sixth in the Premier League table and 11 points off the Champions League places.
But Manchester United announced on Tuesday that "manager Jose Mourinho has left the club with immediate effect".
Watch Premier League LIVE on Sky Sports here ► http://bit.ly/WatchSkyPL
►SOCCER AM: http://bit.ly/SoccerAMSub
►SKY SPORTS BOXING: http://bit.ly/SSBoxingSub