Shearer has been Evans' number one for the last 12 months but has come under fire from fans this season after several errors have led to goals.
Evans insists he is not one to cast players aside on the back of one or two errors but will consider bringing in Collin for his first Millers appearance when Peterborough visit on Saturday.
"Scott's performance levels are not what they were at the back end of last season," he said. "Everyone has bad games, no matter if you are a striker or a goalkeeper, I think I had one back in 1984!
"We accept that he is not on top of his game but he has been doing good things as well. He has made fantastic saves at key stages in games.
"He is still a top-class goalkeeper so people shouldn't be too concerned, they have to remember we are 13 games unbeaten in the league and Scott Shearer has played every one.
"But I understand when people have been raising an eyebrow with the goals we have been conceding, where Scott, by his own admission, could be doing better.
"There's always an opportunity for Adam Collin to play. But you don't get left out of the team here for one or two mistakes. We buy into people long term. Scott Shearer will be a big part of what we do in the season ahead.
"There are some up-sides for playing Shearer and there will be some up-sides to playing Adam Collin and I am looking forward to the debate when I discuss it with my staff."