Fletcher admitted that the confidence of United's players was low during the game, lamenting how their heads dropped when Brajan Gruda gave Brighton the lead in the 12th minute.
"I think you could see the players are fragile but they've got to respond," he said. "Confidence is one of the most powerful things in football so when you don't have it, you have to dig deep and then the confidence comes back. We started OK and then the goal knocked the stuffing out of us. I challenged them at half-time to move the ball with tempo instead of just composure. 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 and get an equalising goal."
Fletcher said that the new manager needed to raise the team's confidence and build unity. "They've just got to come together," he added. "It's only them in the situation and only them that can do something about it. Build the confidence, ground out some results, it might not be pretty at times. I'm sure if the payers show the right reaction, the fans will get behind them like they always do because there is still a lot to play for in the Premier League this season."