United, who are sixth in the Premier League, have played two games fewer than fourth-placed Aston Villa and will look to close the gap to eight points when they play at Chelsea later on Thursday.
With Tottenham Hotspur one place above them in fifth, United have their work cut out to claim a place in Europe's elite club competition.
"I know it will be very difficult because we are not in a good position," said Ten Hag. "But we want to win every game, that is the standard we have here ... We have to catch up. But I also know we have had a lot of problems so I am a realistic man.
"In a competition that is so competitive and the teams are so close in terms of levels with each other, then you need the players to be available to make a consistent team to bring the routines in your way of play."