The Red Devils suffered a 3-1 aggregate loss after Thursday’s 1-1 draw at Old Trafford sent Liverpool through to the quarter-finals of Europe’s second tier club competition.
United have come in for plenty of criticism in recent weeks following their below-par displays and results.
Manchester United legend Keane admits that he has been “saddened” by what he has seen from the Red Devils in recent seasons.
And the former Republic of Ireland international has not been impressed by the players’ attitude in recent games.
Speaking on ITV Sport after United’s exit at the hands of Liverpool, Keane said: “I’m saddened by what I’ve seen from United over the last year or two. It’s like a bunch of strangers have been thrown together.
“When you play for Man United and you put that jersey on, I always felt 10 foot tall but some of these players look like they’re shrinking with the jersey on.
“If you’re playing for Man United, you’ve got to deal with that pressure and that expectation. This group of players is certainly struggling. I know they’ve had injuries and it goes to show how important a fit Wayne Rooney is to this club.
“Where are the characters? Where are the leaders in this group?”
United now turn their attentions towards their Premier League trip to bitter local rivals Manchester City on Sunday afternoon.
The Red Devils are currently sixth in the table.
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