Ospreys have lost centre Jonathan Spratt and number eight Morgan Allen to injury.
Spratt, 28 and capped four times by Wales, has a knee injury while Allen, 24, has "ligament damage".
Allen suffered his injury in Ospreys' European Rugby Champions Cup defeat by Northampton in October and is out for 10-12 weeks.
Spratt will be absent "until the new year", confirmed Ospreys medical performance manager Chris Towers.
"Jonathan has undergone keyhole surgery on his knee, while Morgan underwent an operation two weeks ago, that has a recovery period of 10 to 12 weeks from the date of the op," said Towers.