The Bees were beaten 3-1 at home to Yeovil on Tuesday night following a goalless draw at Bury on the opening day.
Full-back Scott Barron and striker Paul Hayes featured against the Glovers following their recent switch to Griffin Park and Rosler admits they may be lacking some fitness.
But he said: "I'm not starting to have major concerns two games into the season.
"We can say we have had a bad start, two games and one point.
"Both players who joined us lately - Scott Barron and Paul Hayes - have a way to go to catch up fitness-wise. But that is normal, and we knew that. The only way they will get fitter is to play them."