"I would consider it a longshot that he's back in the regular season," agent Joe Bick told The Denver Post (www.denverpost.com) on Thursday.
Cook fractured his right fibula when he was struck by a ball hit by Cincinnati batter Joey Votto during Wednesday's game with the Reds, the Rockies website (http://colorado.rockies.mlb.com) reported.
Rockies officials were uncertain of Cook's future this season.
"This may not be a season-ending thing is my understanding," Rockies manager Jim Tracy told reporters. "Yet, we have to take it a day at a time and see where it all goes."
(Reporting by Gene Cherry in Raleigh, North Carolina)