The former France international played the opening 45 minutes of the contest at Old Trafford but was not seen after the interval, with Victor Lindelof replacing him for the second period.
Ten Hag said after the match that the centre-back «had complaints», and he was therefore not prepared to take a risk when it comes to the 30-year-old's fitness.
«He had complaints. So we didn't want to risk him. We know we have Harry Maguire and Victor Lindelof, good replacements,» Ten Hag told reporters during his post-match press conference.
«So we don't take the risk, but what the complaint is and if it is really bad, we don't know. We have to wait.»
Varane was a part of a Man United defence that conceded twice in the opening four minutes at Old Trafford, with Taiwo Awoniyi sending Forest ahead in the second minute following a breakaway from a corner.
Willy Boly then doubled the away side's advantage in the fourth minute, but Christian Eriksen halved the deficit before Casemiro levelled the scores in the 52nd minute.
Bruno Fernandes then came up with the winner from the penalty spot after Marcus Rashford had been brought to the ground inside the box, with Man United picking up their second win of the season.
The absences of Luke Shaw and Tyrell Malacia led to Diogo Dalot lining up at left-back, but the club are expected to add another player in that area of the field before the end of the transfer window.
There were protests at full-time on Saturday, though, with sections of the fans making their feeling towards the Glazer family clear amid the
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