It got us thinking about goalies who faced Sir Alex's side after leaving the club during the manager's reign.
From our research, we think EIGHT have done this. They must have been named in a United first-team by the boss and played against the Reds later in their career in a senior fixture (not including substitute appearances).
Could you name them? The answers are in the box on the right. Look out for another poser next Thursday.
Thanks to Andy Slater on Twitter, who mentioned John O'Shea but we're not classifying him as a keeper despite his stint in goal against Tottenham!
1. Mark Bosnich
2. Roy Carroll
3. Ben Foster
4. Tim Howard
5. Peter Schmeichel
6. Les Sealey
7. Chris Turner
8. Gary Walsh