Nichushkin left the team during last year's playoffs after a bizarre incident where a woman was found heavily intoxicated in his hotel room when the police were called. Nichushkin was not charged for anything, and instead left the team at the time to enter the Players Assistance Program. It was never confirmed directly by the Avalanche that he did in fact enter the program, but Dater's tweet does imply that was the fact.
Nichushkin will be out indefinitely while in the program, trying to recover from whatever issues may be ailing him. All hockey fans are wishing him the best in his recovery, and a quick return to the ice.