Erik ten Hag eased the pressure on his position with United's deserved 2-1 win over Brentford at the weekend but now faces the unenviable task of taking on Mourinho in an important European clash.
The Portuguese manager has faced criticism himself in recent weeks with Fenerbahce fourth in the Turkish top-flight, though he could soon win back support with victory over his former side this week.
Ahead of the match, there has been plenty of focus on the legendary manager and we decided to take a look back at his Old Trafford spell and all the players he signed during his time at the club.
Here is how we ranked his 11 signings from worst to best:
1. Jose Mourinho signed 11 players during his time at Manchester United
Jose Mourinho signed 11 players during his time at Manchester United | AFP via Getty Images Photo: AFP via Getty Images
2. Alexis Sanchez
It had to be him for all the wrong reasons. Huge wages, huge expectation, low delivery. Just five goals in 45 appearances before he was paid off to join Inter Milan. The only time he found a tune at Old Trafford was when he played the piano in the centre circle. | Manchester United via Getty Images Photo: Manchester United via Getty Images
3. Lee Grant
He only made two appearances during his time at the club but was a well liked and trusted first-team member. Not much more to be said on that one. | Getty Images Photo: Getty Images
4. Henrikh Mkhitaryan
Another player who arrived with high expectations, having won the Budesliga Player of the Year award, but who never really shone in a United shirt. Not really a flop, just a bit underwhelming. | Getty Images Photo: Getty Images