Montanier said that despite picking the players he deemed to be the most fit, his side struggled in the conditions on the night.
"I don't know whether the two sides were suffering from the humidity or the heat, but neither outfit seemed to have much pep, which led to a match with little rhythm," he told Ligue1.com.
"We played a very average game; solid in defence but with little cutting edge up front and we couldn't really hope for more than a point from it. In terms of keeping the ball and controlling play, things went well, but we didn't have the legs going forward to put the Montpellier defence in danger.
"When you can't do any better than that, you concede a draw, but that wasn't what we were hoping for. We didn't rotate the squad for the sake of it. The side I fielded was chosen to be the freshest, in order to get a result tonight. But there's the theory and then the reality - and the reality is decided out on the pitch. We didn't deserve more than a draw."
Rennes are unbeaten in their last five Ligue 1 games.