Leeds could feature Lewie Coyle and Lewis Walters in the cup this week.
Speaking to the Yorkshire Evening Post he admitted Dallas was behind the rest of the squad in terms of fitness, but feels selecting the winger was the right decision.
The Northern Ireland international played well in the 1-1 draw at home to Burnley. He featured for 70 minutes before being replaced by eventual goalscorer Mirco Antenucci.
Rosler said: "We knew that Stuart was a bit behind schedule because he didn’t get enough minutes at Brentford in pre-season.
"It was a little gamble to start him but he justified his starting place. He made a good impact and could have scored two goals."
Leeds hand was forced really by their lack of alternatives out wide on the left, and facing a talented Burnley side recently relegated from the Premier League they had to go for it, and the decision showed positive intent from the new head coach.
Souleymane Doukara had played there in pre-season and drawn praise from Rosler but it was clear he was viewed as a square peg in a round whole.
He could get the chance to stake a claim in the Capital One Cup this week against Doncaster Rovers, with Dallas likely to be saved considering the Whites have a Championship game away to Reading days later.