The team didn't reveal the nature of the violation that led to the suspension. McClain is eligible to return Dec. 10 but Oakland media outlets are suggesting he won't be back in the Oakland lineup.
McClain will lose about $121,000 in salary due to the two-game suspension.
He left Wednesday's practice without taking part and was reportedly asked by the team not to report Thursday.
Raiders Coach Dennis Allen said Thursday, "There's going to be consequences to [McClain's] actions."
McClain, the eighth overall selection in the 2010 draft, is in his third season with the Raiders. He has 60 tackles and one sack in 11 games this season.