Sergio Reguilon was not spotted in Man United's training session on Monday ahead of the Champions League clash with Galatasaray.
The Tottenham loanee featured in the 1-0 win over Burnley with an illness but was ruled out of the double-header with Crystal Palace due to a knock.
Although Erik ten Hag did not refer to him in his team news update in Monday’s press conference, the Spaniard is believed to be out of the Galatasaray game.
Reguilon who is currently nursing a hamstring injury is expected to return in a month's time.
The defender arrived on loan from Tottenham Hotspur this summer, after injuries to Luke Shaw and Tyrell Malacia.
The Spaniard had a promising start to life with United, as he impressed in games against Brighton and Bayern Munich in the Champions League, even though both games ended in defeat.
