United players were seen participating in drills on the Old Trafford pitch shortly after the final whistle.
Keown questioned the decision, suggesting it reflects poorly on the team's management and post-match recovery approach.
On talkSPORT, Keown said: “Does it come across as a punishment though for the players?
“I mean he can do what he wants. It does feel a little bit unprofessional, (like): 'Because we haven't got time in the week to do it, so we are doing a session afterwards'.”
He continued: “It's very unorthodox. It's not the norm, there's recovery, there's stretching, okay? They’ve got nine days before they play their next game.
“But is it about embarrassing the players a little bit? Look, they were awful for large periods of that game.
"So for me it has to be (that) he's so annoyed, there's no time to wait, and no time to lose, because he could be out of a job as well, it’s not beyond the realms of possibility.”