The Belgian forward clashed heads with Southampton’s Wesley Hoedt
The Belgian forward, who has scored 15 times this season, had played every minute in the Premier League before being taken off on a stretcher against Southampton on Saturday following a clash of heads with Wesley Hoedt.
That ruled Lukaku out of Monday’s trip to his former club Everton and he is set to be absent for the FA Cup third-round tie with Derby on Friday too.
Speaking prior to the clash with the Toffees, Mourinho told Sky Sports: “I would say a week (out for Lukaku).
“It’s nothing really important – just a little protection, but no problem.”
There are 10 days between Derby’s visit to Old Trafford and United’s Premier League home clash with Stoke, when Lukaku may be available again.