Ireland forward Iain Henderson is among four Ulster players facing a spell on the sidelines after a bruising victory over Edinburgh on Friday night.
Henderson sustained a "significant" hamstring tear and is now a doubt for the Six Nations.
Peter Nelson (dislocated foot) is out for the rest of the season while Dan Tuohy, who fractured an ankle, will be missing for at least two months.
Darren Cave's shoulder injury will keep the centre out for at least two games.
Ulster back-row Roger Wilson had a back spasm before the Edinburgh game but he is expected to be available for Friday night's European Champions Cup encounter against Toulouse.
It's a grim injury toll for the Irish province resulting from the hard-fought 14-7 win over the Scots at Kingspan Stadium.
Henderson will be reviewed by a surgeon and a return date will be clearer after this consultation.
Full-back Nelson dislocated his left foot - it was relocated in the medical room at Kingspan Stadium and he will have surgery when the swelling subsides.
Tuohy also sustained ligament damage and the Ireland lock may require surgery while Cave suffered an AC joint injury.