It followed a clash of heads with his old Leinster team mate, Wasps' centre Brendan Macken. As a dazed Sexton was receiving treatment, the game continued and he broke off to make another tackle, only to be later helped from the pitch by a Leinster medic once play stopped.
Leinster later tweeted that Sexton, who has suffered a catalogue of concussions in recent years, had failed his head injury assessment and would enter 'return to play' protocols.
Coach Leo Cullen told RTE 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."
Yet what should have been a day of celebration for the 30-year-old, named Leinster captain for the first time on his 100th start, ended with fresh concerns over his susceptibility to concussion just a fortnight before Ireland open their Six Nations defence against Wales.
(Reporting by Ian Chadband)
