Redmond is set to be ruled out for up to three weeks with an ankle injury.
The winger went down unchallenged during Tuesday evening's Carabao Cup win over Fulham at Craven Cottage and was seen leaving the ground on crutches wearing a protective boot.
"In the moment, it looks that he seems to be out for two, three weeks, I think," Hasenhuttl said of Redmond.
"It can be longer but with good rehab - the next 10 days, he has to wear a shoe that doesn't move his ankle - and then it can be quicker.
"He will be a massive loss for our team, for sure. He can make a difference and I'm happy that it's not worse because it could've been and then the impact would have been worse for us.
"Every game he is missing isn't good for us."