Ashley Fletcher is expected to be out for two to three weeks and will not be available for Middlesbrough’s home clash with fellow play-off contenders Cardiff.
The striker was forced off during the midweek defeat to Bristol City in what was just his third start since returning from a five-month absence following a hamstring operation.
It is not a recurrence of that injury but the club are waiting on the results of scans to determine exactly what the issue is this time and how long he will be out.
Yannick Bolasie and Marcus Tavernier are both making progress but Saturday’s match will come too son for them as Boro boss Neil Warnock prepares to face his former club.
Cardiff forward Junior Hoilett could return after missing four matches with a calf injury.
Midfielder Joe Ralls, who has been out for more than a fortnight, remains a doubt as he continues to recover from an ankle injury.
On-loan Arsenal defender Jordi Osei-Tutu could return to first-team training in a couple of weeks having not played since October.
Forward Lee Tomlin, also absent for four months, has stepped up his recovery from a groin problem with a second outing for the under-23s.