Louis van Gaal still believes Manchester United can finish in the Premier League's top four but conceded their hopes of Champions League qualification suffered a significant blow in the 3-0 defeat to Tottenham.
Kick-off was delayed by half an hour at White Hart as the United team bus got stuck in London traffic but its inhabitants endured far greater discomfort after Dele Alli scored the opening goal 20 minutes from time.
Toby Alderweireld headed a second and Erik Lamela netted a superb third as Spurs demolished their tardy visitors within six thrilling minutes.
United lie four points behind fourth-placed Manchester City having ceded the ground they gained by winning last month's Manchester derby.
"Every team can lose to everybody so still we are in the race, but of course when you lose a game you have to close the gap again and that's more difficult," Van Gaal told Sky Sports.
"I think that Tottenham is a great team and I've said that also in advance of this match. Until the first goal we were the better team and also had a big chance for the first goal.
"To lose by three goals is a big negative result but the way that we have played until the first goal was good."
Neither side registered a shot on target during a dour first half but Van Gaal rued a 62nd-minute miss from Anthony Martial before Tottenham's decisive salvo.
"I think the better chance was with us, with Martial - that was big chance," he said.
"We gave the goal away with miscommunication and then you know what happened. Within five minutes we were out of the game.
"We didn't clear our heads. I think it is strongly expressed because the second goal is a set play. One of our best headers loses that duel.
"It is also a fantastic header from Alderweireld but it is happening and it cannot happen."
Van Gaal explained his slightly perplexing decision to field Ashley Young as a centre-forward on his return from a lengthy groin-injury absence, having replaced teenage striker Marcus Rashford with the England international at half-time.
"I wanted more running in behind because in the first half we didn't have an attacking point there."