Johnny Sexton faces a race against time to be fit for Ireland’s opening Six Nations tie with Wales having come off after just nine minutes of Leinster’s Champions Cup match with Wasps.
The out-half, captaining the province for the first time in his 100th appearance, was replaced by Cathal Marsh after a clash of heads early in the Pool 5 defeat.
The ex-Racing Metro man has a history with concussion injuries and may have been replaced as a precaution given that Leinster were already out of contention in the competition.
Ireland start their Six Nations campaign against Wales in Dublin on Sunday, 7 February.
After the game Leinster tweeted: "Johnny failed HIA, enters return to play protocols."
Coach Leo Cullen told RTÉ Sport: "He just got a head knock. We’ll get him assessed and see how he is but he’s up and about in the dressing room fine there.
Prop Marty Moore, cover for Mike Ross, also went off with a hamstring injury.