United's last hope of silverware this season went up in smoke on Monday as Danny Welbeck returned to haunt his former employers with the winning goal in a 2-1 triumph that sent holders Arsenal into the FA Cup semi-finals.
That was only United's second defeat in their past 11 matches in all competitions and followed back-to-back league victories over Sunderland and Newcastle United.
Rather than be downbeat about United's chances of clinching a top-four berth, manager Van Gaal has seen a good reaction in training.
"I have the same confidence [of reaching the top four] as before," he said.
"I'm very pleased with the reaction and I hope we can show that against Spurs - the first of 10 matches in the rat race."
If Rojo is unavailable it will leave Van Gaal short at the back as fellow defender Jonny Evans starts the first game of his six-match ban for spitting at Newcastle's Papiss Cisse. Angel di Maria is also suspended after being sent off against Arsenal.
Tottenham travel to Manchester seeking a third-consecutive victory over United at Old Trafford, which would move them level on points with Van Gaal's men.
"We believe we can win," he said. "You never think before a game that it is possible to lose.
"You are always focusing on getting the three points and are never thinking about losing.
"Our pressure is inside us, in the group. We want to win every game.
"Maybe Manchester United has history, but our mentality is to compete and try to win the game. Man United is not my problem."
