Roberto De Zerbi criticized Mason Greenwood following Marseille's 3-0 loss to Paris Saint-Germain in Ligue 1 on Sunday evening.
The 23-year-old has made a bright start to life in France following his move from United in the summer in a deal which could be worth up to €31.6 million (£26.6m).
However, Greenwood had a game to forget at the weekend as he was substituted at half time with Marseille trailing PSG by three goals.
When asked about his decision to replace Greenwood at half time, De Zerbi said: ‘I didn’t like the way he played tonight.
‘I think he was having a bad day. He gave us a lot of goals and points but when you’re at Marseille, if you want to fight for the championship, you have to push in every match.
‘You can’t say you’re doing a good performance by scoring two goals and then having a bad patch the next match. It’s not possible.
‘He’s a good player but I expected more from him tonight. But not only from him. I always expect more in general.’
The defeat has left Marseille third in Ligue 1, six points behind leaders PSG.
Joao Neves opened the scoring for PSG before Marseille were reduced to 10 men when Amine Harit was sent off.
Leonardo Balerdi’s own goal doubles PSG’s lead before Bradley Barcola struck five minutes before half time.
Greenwood, meanwhile, has scored six goals in his first nine Ligue 1 appearances for Marseille and has already been hailed as one of the best players in the French top flight.
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