Leicester backs coach Paul Burke said he is unsure how long Toby Flood will be on the sidelines with a head injury sustained on Saturday.
The England fly-half spent the night in hospital after he was taken off during the first half of the pre-season clash with Ulster at Welford Road after being struck in the face by Irish lock Dan Tuohy.
Leicester's medical team spent 12 minutes working on an unconscious Flood on the pitch before he was taken off on a stretcher and the 28-year-old didn't come around until he was in the Leicester Royal Infirmary.
Flood has undergone checks for concussion and after such a serious blow he is expected to miss next weekend's Premiership opener against Worcester at Welford Road.
Burke wouldn't discuss how long Flood would be sidelined as the reigning champions await a diagnosis on the extent of the head injury.
"It's too early to put any time frame on the injury," he said.
"We will get the advice from the medics and take it from there."