Lock Tom Franklin left the field early in the second half in last Saturday's game against North Harbour with a groin strain.
Coach Cory Brown said Franklin was not going to play this Saturday against Canterbury in Christchurch and a return date was unknown at this stage.
''Groins can be a hard thing to come right. They can take a while. We're not too sure at this stage when he'll be right,'' he said.
''We might be looking at two to three weeks but it can be hard to say.''
Brown did not think the injury came from Franklin playing too much but was just part and parcel of playing a physical sport.
It is a blow for Franklin (26) and Otago as the lock was in some top form.
''He has been in outstanding form for us both on attack and in defence. Everything he has been doing on the field has been great for the team.
''But his absence just gives the chance for someone else and Josh Dickson will now get the chance to call the lineouts which will be good for his development.''
Blair Tweed will come back into the starting side, Brown said. Tweed is just getting over a shoulder injury but should be right.
No8 and captain Paul Grant will be the back-up lock on Saturday and Otago will have two loose forward reserves on the bench.
Franklin is a genuine chance to make the All Blacks end-of-year tour.
He was called into the All Black squad for the June internationals as cover for an injured Sam Whitelock but did not get on the field.
He has been a standout for Otago and the Highlanders this year and has taken the most lineouts of any forward in the competition this season.
The other injury concern surrounds fullback Michael Collins, who left the field with a calf strain against North Harbour but did train lightly yesterday.
Collins (23) is coming off a season with the Llanelli Scarlets so has had plenty of rugby in the past 12 months.
Brown said he was mindful of the amount of rugby Collins had played in the past year and would not push Collins to play if he was not right.
Collins has looked sound at the back for Otago and Brown said he had all the skills to play at the next level.
The likely replacement for Collins if he is not right is Tony Ensor.
Otago is now the only unbeaten team in the Mitre 10 Cup after Manawatu beat Canterbury on Saturday night in Palmerston North.
Otago last beat Canterbury in Christchurch in 2005.
