Mauricio Pochettino admits it will be "difficult" for Tottenham to finish in the top four of the Premier League after Manchester United opened up a six-point gap on them.
The Spurs boss was unhappy with his side's performance as they went down 3-0 at Old Trafford on a day they could have gone level on points with United.
Goals from Marouane Fellaini, Michael Carrick and Wayne Rooney saw Spurs off, and Pochettino insists this sort of performance cannot happen again.
He told Sky Sports: "It will be difficult [to finish fourth] because we are fighting with big sides.
"It was a very bad day for us. I think that we all agree together in the changing room that our performance was poor.
"Our performance was poor, and I think we need to analyse why. We are disappointed because we never show our quality, our way and our philosophy."
Despite the defeat, Pochettino insists Spurs players should not dwell on the performance, and must form a new fight for the top four with nine games remaining.
"For us, we must not think too much about this result and try to fix the problem. It was a very bad day for us," added the Argentinian.
"I think that we feel too much we didn’t start a good game and we gave Manchester United the opportunity. We need to fix the problems."
Pochettino brought Andros Townsend off in the 30th minute to be replaced by Moussa Dembele with Spurs 2-0 down, and the Argentine admits it was a tactical change.
"After being 2-0 down after 20 minutes, it was difficult to keep the ball in our way, so we changed Dembele, and it was a tactical substitution.
"We tried to play in our way and keep the ball down."