Graves was diagnosed with a concussion Friday, according to Michelle Crechiolo of the Penguins' official site.
Graves was injured late in the first period Thursday versus Columbus and did not return. The 28-year-old blueliner has three goals, 11 assists, 72 hits and 142 blocked shots in 70 appearances this season. John Ludvig will likely replace Graves in the lineup Saturday, as the Penguins get a return match against Columbus. Graves should miss at least a week with the concussion, and it's possible that his season could be over.