Manchester United manager Sir Alex Ferguson has admitted it is "a bad blow" to lose Antonio Valencia for four weeks with a hamstring strain.
The South American had only been on the field for 10 minutes following his introduction as a second-half substitute. However, after playing an integral role in Javier Hernandez's second in United's 2-0 Europa League win over Ajax in Amsterdam, Valencia was immediately replaced.
And Ferguson confirmed the news was grim, saying: "It is a bad blow for us. He has a hamstring injury unfortunately. It will be four weeks."
Valencia has been one of United's best players in recent weeks but will now definitely miss the crucial Premier League showdown with Tottenham at White Hart Lane on March 4.
If there was a positive it was that Nani and Ashley Young were amongst those to return to action.
Young marked his first appearance since Christmas with his fourth goal of the season, breaking the deadlock after a dismal first-half display.
"The result was better than the performance," said Ferguson. "The first half was disappointing. We found it difficult to get rhythm and speed to our game. Ajax pressed the ball very well and played nice football.
"We had to waken up in the second half because we were making it difficult for ourselves.
"The second half improved and we made some good opportunities. We deserved to win and you can't complain too much when you win 2-0 away from home."
Next Thursday's second leg should be a formality, allowing United to book a last-16 encounter with either Lokomotiv Moscow or Athletic Bilbao.