Get the United transfer latest, team news, match updates and analysis delivered straight to your inbox every day for free Ole Gunnar Solskjaer felt Manchester United needed a third centre-back to counter Young Boys' wing play in the second-half of their Champions League defeat.
Solskjaer reacted to Aaron Wan-Bissaka's 35th-minute expulsion by sending on right-back Diogo Dalot for Jadon Sancho, and Varane was told just before the first-half ended he would be sent on for the second-half.
Donny van de Beek made way for Varane and United switched to a back three, with the Frenchman in between Victor Lindelof and Harry Maguire.
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