Roos had a debut to forget for the Millers as he shipped four goals during Saturday's harrowing opening-day defeat to MK Dons, looking shaky throughout.
Evans is only pointing the finger at the Dutchman - who was making his Football League debut at the weekend - for the Dons' fourth goals, though, and has backed him to come back stronger against the League Two outfit on Tuesday.
Although revealing he will make changes to his side, one of those will not be in goal.
"The goalkeeper should do better for the fourth goal, but when you break them down, for the first three goals I think it would be harsh to blame him, the quality of defending in front of him was not very good," Evans insisted.
"The first goal he gets a hand to, the second goal gets fizzed across goal and Danny Collins deflects it and it ricochets through his legs and crawls over the line, it’s cruel really.
"From a concentration point of view he had a few pass backs that go to his wrong side and his skews them away.
"It probably has people looking at his performance more than they should.
"For the fourth goal I’d accept that the big fella gives him half a yard too much at the near post, but it’s a finish with some power.
"I don’t think by any stretch he was the worst performer, there was a lot worse defending in front of him. I will say now, he will play in goal, don’t worry about that, he’s a good goalkeeper."
Should Steve Evans stick with Kelle Roos for the Cambridge game?
There could be widespread changes elsewhere on the pitch, though, as Evans looks to get minutes into the legs of his players.
Joe Mattock is not expected to be rested, with him due to return to training on Wednesday, while Farrend Rawson played for Derby's Under-21s side last night as he builds up his fitness following a groin injury.
Kirk Broadfoot is suspended, but Jordan Bowery, Jonson Clarke-Harris, Lewis Buxton, Emmanuel Ledesma, Lee Frecklington, Paul Green and Frazer Richardson are all hoping to be named in Evans' starting XI.
"We will make changes because it was always the plan," the boss said.
"There won’t be the wholesale changes that everyone expects because you lose 4-1 at home, you have to have a sense of perspective on things.
"That game could have been wholly different had we taken our chances.
"But there will be changes because one or two players need to get on the pitch, one or two need game time and one or two players need to come out that have had quite a bit of game time.
"We need to make sure we get everyone in the squad as fit as we possibly can for Nottingham Forest. That’s not to devalue the cup in any shape or form."
Is Evans right to stick with Roos or should Adam Collin come into the side? Have your say below.
