Tottenham Hotspur manager Mauricio Pochettino has warned Manchester United that they could find it difficult to juggle Europa League commitments with their Premier League campaign.
Louis van Gaal's side dropped into the second-tier European competition following Tuesday night's 3-2 defeat to Wolfsburg in the Champions League.
Tottenham are already in the competition and will become Group J winners if they get a point against Monaco this evening.
"It's a big, big difference," Sky Sports News quotes Pochettino as saying. "When you play Thursday and Sunday, it can affect the mentality and the psychology of the players. Thursday night - [long] travel and you need to play Sunday afternoon. Always for the player it affects them. Football is [supposed to be] Saturday three o'clock.
"It's never easy. You never know how it will affect you, but it's true that, for now, United must feel very disappointed because they had the possibility to go through to the next round.
"It's true that's a different competition and you have to change your approach. It's tough for them, but you never know. It's about how you develop your game."
In the Premier League, United are currently fourth in the table.