Leicester and England fly half Toby Flood required hospital treatment after taking a blow to the head during a pre-season game against Ulster on Saturday.
The 28-year-old Tigers captain suffered the injury in the 10th minute as a result of being struck in the face by second row Dan Tuohy, who was sin-binned for the offence.
Flood lay motionless on the ground and required oxygen as the game was stopped for 12 minutes.
The injury gives director of rugby Richard Cockerill cause for concern as the Tigers open their Aviva Premiership campaign against Worcester Warriors next Sunday.
