The 18-year-old was shown a straight red card in United’s Capital One Cup defeat to Doncaster Rovers following an ugly two-footed challenge.
Cook has since promised there will be no repeat ahead of what is likely to be both his return to the team at Derby County and that of Luke Murphy.
Rosler, though, does not want Cook to lose any of the desire and determination that has characterised his first year in the United side.
“Lewis is a fantastic boy,” said the Leeds head coach. “Of course, he has to learn now and then to maybe be a little bit more cautious.
“But, in general, I just want to keep him as he is because he has made big strides. We have missed him, like we miss all of our players when they are injured and I think Lewis was in good shape.
“I don’t want to take away his desire to get on the ball and to play the football he can play.”
Cook’s return is a boost for Rosler as Leeds go in search of their first victory of the season against a side that has also drawn the first four games.
United had been hoping to have Fernando Forestieri on board by tomorrow’s trip to the East Midlands, but a £3m move has stalled amid interest from Sheffield Wednesday.
“I cannot update you because I am not involved in any negotiations whatsoever,” said Rosler when asked if the Italian was still a target.
“I know as much as you know. Obviously, we have shown an interest in the player but where it is at this time I can’t tell you. I don’t know where we are.
“I know there was a general interest. I think everybody knew that. But where we are now, (yesterday), I can’t tell you.”
Rosler was at Bury on Tuesday night watching Leicester City defender Liam Moore, who is understood to be available on a season-long loan.
A move for Moore could come at the end of a week that saw Giuseppe Bellusci linked with a possible return to Italy.
Rosler added: “I am personally not aware (of bids for Bellusci). I have not been told that there is a club who’ve shown serious interest.
“At the moment, I have no knowledge of any player in our football club who has serious interest (shown in them).”