Jadon Sancho was absent from the Manchester United squad to face Brentford due to personal reasons, Ralf Rangnick confirmed.
The winger came on as a substitute in the 2-2 draw against Aston Villa on Saturday but hasn't travelled to the capital in United's first visit to the Bees since 1947.
Edinson Cavani was also out of the United squad having withdrawn after training on Tuesday with an injury. He was replaced by Cristiano Ronaldo in the starting XI, while Marcus Rashford and Anthony Martial are back on the bench.
United could only field eight substitutes at Villa Park, but were back to a full quota at Brentford, although that includes Dean Henderson and Tom Heaton, while Scott McTominay replace Nemanja Matic in the starting XI.
"Edinson had to drop out after training yesterday. He had some muscular problems, I'm happy to have Cristiano back," said Rangnick before the game.
"Luke also unfortunately had to pull out after yesterday’s training. He had some hamstring problems after the training session. And Jadon misses out for personal reasons.
"Scott was suspended against Villa, so I decided to play him from the start."
United have won just one of their previous five away games in the Premier League and could face a tricky evening at the Brentford Community Stadium, with Thomas Frank's side bloodying the noses of Arsenal and Liverpool already in front of their own fans, as well as giving Manchester City a close game.
“It won’t be easy to play here, quite a few other teams had problems here," said Rangnick. "We’re fully aware we have to play physically, mentally and tactically at an extremely high level. We did that at Villa Park for 75 minutes, today we have to show up with this kind of football for 90 or 95 minutes."
United got back to winning ways with a 3-1 win against the Bees, courtesy of strikes froma cademy trio Anthony Elanga, Mason Greenwood and Rashford.
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