Mourinho has won three Premier League titles across two spells with Chelsea, while he claimed the Europa League and Carabao Cup in his first season at United, finishing runners-up to Manchester City in the league in 2017-18.
While City, Liverpool and even Tottenham Hotspur have been thrilling fans with their swashbuckling approach, Mourinho has become the arch proponent of "parking the bus" - a phrase he introduced to English football's lexicon when complaining about opponents packing their defences to foil his exciting Chelsea team.
Mourinho "has left the club with immediate effect", the statement read.
It may be unusual for some United fans to countenance but former Arsenal boss Arsene Wenger is at 20/1, the same as Bournemouth manager Eddie Howe.
The 49-year-old led France to their second World Cup this year and it remains to be seen if he would be tempted away from the Les Bleus where he has a contract until 2020.
The final months of Mourinho's time in charge were marked by high-profile clashes with star players Paul Pogba and Anthony Martial, and apparent discontent over the club's failure to sign a defender in the summer.
March 13, 2018 - Sevilla knock United out of the Champions League at the round of 16 stage, winning 2-1 at Old Trafford after a goalless first leg in Spain.
It is United's worst 17-game start to a league campaign since the 1990-91 season, and the team now has a goal difference of zero.
In some of Mourinho's final public comments as United manager, he said "for sure we are going to finish in the top six. but the better we can get is fourth position".
Manchester United had an underwhelming start to the current season, but a 3-1 loss to league-leaders Liverpool on Sunday might have secured Mourinho's departure.
"I am really, really happy with the players that I had on the pitch, with their attitude, with their effort".
"Obviously I'd be lying if I said you are not disappointed when you are on the bench - every player is disappointed when he's on the bench".
Mourinho said the club's difficulties with injuries had been a long-term issue.
However, his style might be too attritional for a club looking to move on from a manager who picked fights with most of his squad and with the board.