Keane, who captained United in his time and won seven Premier League titles with the club laid into Mourinho, who took the club into the Europa League quarterfinals with a 2-1 aggregate victory over Rostov on Thursday.

Mourinho was an unhappy man after the game, when he raised alarm bells about fatigue in his players and the fixture pileup for United.

United are due to play their third game in seven days -- they were beaten by Chelsea in the FA Cup on Monday -- and have a league game against Middlesbrough this Sunday.

Mourinho claimed United will "probably lose on Sunday [against Boro]" and that they have "lots of enemies."

Roy Keane won the Premier League seven times as a Manchester United player.

Keane was not impressed with the United manager, launching a tirade questioning Mourinho's ability to manage his former club.

"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."