Keane, who won seven Premier League titles at Old Trafford, was angry with Mourinho after he complained about the fixture list, following their 1-0 win over FC Rostov in the Europa League on Thursday.
“I’ve never heard so much rubbish in my life. Why do we have to listen to that garbage? It’s just utter nonsense what he’s talking about,” Keane told ITV.
“He’s manager of Manchester United, one of the biggest clubs on the planet, the squad he’s got, the players and he keeps moaning about fixtures and fatigue.
“We were just looking at some of the cup draws they’ve had. They’ve had an easy way in the cups, some good draws, a lot of home draws, and the guy is talking absolute nonsense.
“I’ve never heard so much rubbish in my life. Maybe the club is too big for him, he can’t deal with all these demands at the match. What matches? Man United reserves could’ve won that game”, he added.