Fletcher was booked after the final whistle for confronting referee Simon Hooper and later made clear his anger was driven by what he described as inconsistent officiating.

United's difficult season took another blow as the Seagulls claimed victory, prompting boos from sections of the home crowd. Fletcher headed straight for the officials at full-time and was shown a yellow card after a heated exchange.

Explaining his reaction, Fletcher focused on the red card shown to teenage winger Shea Lacey, who was sent off after receiving two yellow cards late in the game.

"Shea Lacey's yellow card is ridiculous compared to the fouls that we had against us all game, which ultimately then the lad makes a mistake and is sent off," Fletcher said. "For me it is poor refereeing."

Lacey, 18, had been introduced in the 62nd minute and looked lively, but his night unravelled quickly. He was first booked in the 87th minute for a late challenge on Brajan Gruda. Just two minutes later, he received a second yellow for dissent after slamming the ball into the ground following a decision against him as Ferdi Kadioglu shielded the ball out of play.

The youngster left the pitch devastated, heading straight down the tunnel. Fletcher was keen to protect him afterwards.

"He's disappointed because he cares and he understands and he knows he will learn from it," Fletcher said. "There is no doubt about his talent and it was a steep learning curve today, but we believe in Shea."

Lacey later apologised, admitting: "I let everybody down tonight. I shouldn't let my emotions get the better of me."

On the performance, Fletcher added: "Mixed performance. We started OK and then the goal knocked the stuffing out of us. When we got back to 2-1, I thought, 'here we go', the crowd was up, the energy was up, but we couldn't get it over the line."

United are now out of all cup competitions and sit seventh in the Premier League, three points off fourth, with Manchester City visiting Old Trafford next Saturday. Fletcher insisted the players must respond, saying: "This team is still good enough to achieve success this season, but they have to dig deep."

Arne Slot refuses to gamble vs Barnsley as Liverpool name strong FA Cup squad