Liverpool legend Jamie Carragher could not help but twist the knife following Manchester United's FA Cup exit at the hands of Middlesbrough on Friday night.

The Red Devils were dumped out by the Championship side on penalties, with Anthony Elanga firing the decisive spot-kick over the bar after the fifth-round clash finished 1-1 after extra-time.

It was another night to forget for United
But it was a memorable one for Middlesbrough

Ralf Rangnick's side were guilty of squandering numerous guilt-edged chances: Cristiano Ronaldo missed a first-half penalty, while Bruno Fernandes spurned a glorious one-on-one opportunity.

Reacting on Twitter, Carragher recalled a heated debate with Man United legend Roy Keane earlier this season, when the former midfielder claimed Ronaldo had been signed to help the Red Devils win cup competitions.

Carragher tweeted, alongside a confused emoji: "Roy Keane told me Man Utd had signed Ronaldo to win the #FACup."

Keane, meanwhile, was left bemused himself in the studio at Old Trafford after watching his former side's wastefulness.

"Over the last couple of home matches they have only scored one goal and one obviously again tonight," he said on ITV Sport.

"I was talking about Man United finding a way to win the game but what did they do, they found a way to lose the game. That's not a good sign.

Fernandes missed a glorious chance
Ronaldo failed to convert from the spot in normal time

"You have to be critical of United. First half fantastic, but they are playing a Championship team. To lose to a Championship team at home in the Cup, it's obviously not good enough."

Asked if it is impossible to go full-throttle for 90 minutes, Keane said: "I think it is, but then that's when you have team management.

"Of course, Middlesbrough were going to come with a bit of pressure in the second half, but you control it.

"Even with the goal they conceded, they were outnumbered, players weren't getting back, and that's where I go back to it, you need a bit of leadership, the character to go, 'Ok we have dropped off for 10 or 15 minutes but we are still up against Middlesbrough, we'll still slip back in and find a moment'.

"But Fernandes's miss there, he has to score, there is no logic to that miss, he has got to hit the target."

And Keane believes this will only pile more pressure on Rangnick and his players as they try and challenge for the Premier League top four.

Carragher reignited this feud with Keane

He added: "Changes the mood, the mood in the ground tonight. No doubt the fans will be leaving the ground…. We were fully expecting them to beat a Championship team, Man United at home, but no.

'It adds more and more pressure for the upcoming games.'