The Carolina Hurricanes defender was diagnosed with a concussion during Game 4 against the Ottawa Senators on Saturday, the team announced on Sunday.
The Senators’ Tyler Kleven levelled Nikishin during the Hurricanes’ 4-2 series-clinching victory. He stayed down on the ice for some time, looking visibly dazed, before being helped off the ice.
Nikishin travelled with his team back to Raleigh, where he will continue the NHL’s protocol for a safe return to play.
The 24-year-old was held pointless in the first-round sweep of the Senators, but finished as a plus-one in the series.
The Hurricanes are awaiting the winner of the Pittsburgh Penguins and Philadelphia Flyers in the second round.