Warriors face defending champions Scarlets at Scotstoun on Friday night for a place in next weekend's final in Dublin.
Leinster host Munster in the other semi-final on Saturday.
Speaking to BBC Scotland, Rennie said: "You've got to put yourself in the race. I think a pass mark is making the semis, anything below that would've been a massive disappointment."
Ali Price, Alex Dunbar and Huw Jones have not made the match-day squad despite being fit and available, having struggled with injuries and form respectively after the Six Nations.
Rennie says those players have missed out due to the good form of others rather than their own recent displays.
"We've just picked on form," the New Zealander explained. "We're fortunate we've got a lot of depth in those key positions.
"Nick (Grigg) and Sam (Johnson) have been really strong for us throughout the year and George Horne has had a fantastic season and gets to start.
"I thought we managed (the Scotland contingent) pretty well. We gave a lot of those guys a couple of weeks off rather than coming straight back in and we've had another couple of weeks off."
Warriors have lost three of their past four league matches, but Rennie believes his side are ready to find the top gear they will need to overcome a Scarlets side that reached the semi-final of this season's European Champions Cup.
"We know it's do or die so we expect a great performance out of them," Rennie continued.
"We've had three weeks to prepare and we've mixed in some good fun with some hard work. There has been a lot of clarity around expectations.
"I think we're in a really good spot. I think the weather is going to play its part, we'll have a massive home crowd so we're really looking forward to it."
Scotstoun Stadium's capacity has been temporarily expanded to 10,000 for Friday's match. It will be Finn Russell's last home match in Glasgow colours before his summer switch to French side Racing 92.
Rennie hopes Glasgow can send the Scotland fly-half on his way by extending their perfect home record, which has yielded 10 wins from 10 PRO14 matches this season.
"There are a lot of motivating factors," the former Chiefs coach added.
"Last game at home for guys like Finn. I know the guys will bar up, but there are lots of reasons to perform. We've prepared well so we'll hopefully give them a decent send off from here.
"We've been good at home and the crowd makes a massive contribution to that. An extra 2,500, good weather and a good occasion.
"You've got two really positive sides who I think will play footy so it should be great."