And Keane, who won seven Premier League titles with the Red Devils, has bemoaned the lack of passion displayed in their dismal run.
While the ongoing fallout of Pogba and Mourinho has stolen most of the headlines, the Republic of Ireland assistant coach feels the entire squad is letting the club down.
The club's highest paid player, Alexis Sanchez, lost the ball a staggering 26 times in the mid-week stalemate with Valencia, and Keane eluded to the fact that fallouts and disagreements shouldn't hinder the efforts on matchdays.
"But what you do as a footballer, and I've had one or two disagreements, when you cross that line you play for your team.
"I don't care what fallout you've had with your manager, I don't care if you've been at each other's throats. That is part of the industry.
"People do fall out. Unfortunately, when you're at Man United – one of the biggest clubs in the world – things will get exaggerated.
"And if you're a footballer for Manchester United, you put that jersey on, you walk out and you don't give 100 per cent because you might be upset with somebody, then good luck to Mourinho with this stuff.
"I'm not talking about Pogba. I'm talking about players in general. Players who get upset with a manager or a coaching staff and think ‘I'm not going to train properly because somebody upset me.' There are a lot of cry babies out there," the 47-year-old added.
"When you walk out on that pitch, you're playing for your pride, you're playing for your family, you're playing for your city, whatever it might be.
"Don't get that worried about what the manager's said about you, or the coaching staff, you get out there and play.
"You can follow it up after the match, but when the game's going on, liven up. Play with pride, play with energy, play with spirit.
"Hopefully, play with a bit of skill. But on your bad days you roll your sleeves up and you fight for that jersey."