Orient are top of League One after a record-breaking seven wins out of seven, and head to Griffin Park for a mouthwatering London derby on Monday night.
"I am not surprised Orient have started well," said Rosler, whose side are currently ninth.
"They had a good run at the end of last season. They continued this season.
"It will be a big game. We normally do well against teams around us and above us.
"I am looking forward to next Monday."