Krug injured his left ankle late in the third period of the Bruins' 4-3 overtime loss Friday. He will undergo additional testing to determine the full extent of the injury, the team said.
Krug has three goals and nine assists in 11 postseason games, the most of any of the Bruins defensemen.
He was seen leaving TD Garden on crutches and in a walking boot after Friday's game.
Holden has played in only one game this postseason, logging 12 minutes of ice-time. The Bruins are also without defenseman Brandon Carlo, out since the end of March with an ankle injury.