Although the Red Devils boss did not aim his attack at specific individuals, he was quick to criticise the fringe squad members who were given a runout against the Seagulls.
"It was not good enough," he told Sky Sports News. "The players that replaced others did not perform at a good level and when individuals do that it is difficult for the team to play well. Maybe now you will not ask me why A, B and C do not play so much.
"I knew what was going to happen and I told them, but that is what we got.
"The attitude from the first minute and especially in the first half, they had more appetite. I did not succeed in persuading my players that getting four more points is important. it is for me, but perhaps not for them.
"I wouldn't say disappointed. I know them. I thought that the possibility to start the game and give reason would give them something. You have the answer now when you ask 'why always [Romelu] Lukaku?'. We are probably not as good as people think we are individually."
United remain second in the league table following their defeat on the south coast.