Rennie gave more positive updates on lock Jonny Gray, hooker Fraser Brown and wing Tommy Seymour, who was also on the Cardiff casualty list last weekend, all of whom should be in contention for next week’s home game against Benetton Treviso.
Dunbar, who has been no stranger to injuries down the years, left the field during Saturday’s 20-19 win at Cardiff Arms Park and Rennie said: “Alex injured his knee last week so we will know more about the severity of that over the next two or three days. He could be out for a little while.
“We are expecting Fraser back next week so all being well he will be in the mix for Treviso. Jonny Gray will be very close around that time, too.
“Tommy has got a slight groin issue. The top of his quad. It is a little bit tight. We decided to play it safe and he will be fit for Treviso.”
Tonight represents Glasgow’s biggest game of the Guinness Pro14 season so far and, as well as looking to make it four wins in a row, the Warriors will be looking to avenge the frustrating four-game losing streak to their old Irish rivals last season, which included two European defeats. “We have not spoken about it,” Rennie said. “I am of the belief that history counts for nothing. It is what we do in the 80 minutes that will be key. I am sure there will be personal motivations for individuals who played those games.
“They were tight games. Bar one they were arm wrestles that could have gone either way. We are happy in one perspective [so far this season], we have won games without playing at our best, have shown a bit of character and found ways to win. That attitude is going to be important tomorrow night.
“We are happy we won the first three, but we are measuring things by our own standards. We have defended with a lot of character and only conceded two tries. But we haven’t held on to the ball for long enough.
“Last week we created a lot of opportunities but just weren’t clinical enough and that has probably been the theme of the first three weeks.
“Now, we are going to come up against a very strong defensive side. It will be a great test for us. If we can hang on to the ball tomorrow night then we can put them under a bit of pressure.”
Skipper Ryan Wilson returns for the sold-out top of Conference A clash, while Ali Price takes back the scrum-half jersey from Henry Pyrgos.
Wing Rory Hughes and centre Peter Horne are also back in the backs, while Rob Harley could feature for the first time this season off the bench after recovering from an ankle injury.
Loosehead Ryan Grant is back training with his former club and Rennie confirmed that he would be staying on as injury cover.
The former Lion is now a free agent and was involved with Edinburgh in pre-season. “With Oli Kebble out injured, we are looking at options,” said Rennie. “We have brought him in and he will be in for a little while as cover.”