The Oilers announced Friday that Green has a sprained MCL. He was hurt in a loss against Vegas on Wednesday.
The Oilers acquired Green in a trade with the Detroit Red Wings early Monday, hours before the NHL’s trade deadline.
Green was playing his second game with the Oilers when he suffered the injury.
The 34-year-old Calgary native has three goals and eight assists in 50 combined games with Detroit and Edmonton this season.
The Oilers (33-23-8) entered Friday night’s action holding the third and final playoff spot in the Pacific Division.