The Astros signed Crain to a one-year, $3.25 millon contract last winter to bolster their bullpen, but the recovery has taken longer than anyone expected.
Crain hasn't completely ruled out pitching in September, but it's extremely unlikely.
"I'm making progress, but in the big scheme of things, time is running out," he said. "We'll see. I'll keep grinding until the finishing bell rings. I'm definitely getting better and making progress, and whether it's going to be enough time to get into a game, it's hard to say. We'll see."
Crain, who hasn't pitched since last July, would like to play for Houston next season, but he'll have to get healthy first. General manager Jeff Luhnow said on Monday that the club has looked into its medical due diligence when it comes to signing injured players.
"I've done all I can do in the big scheme of things," Crain said. "It's unfortunate time is running out. All I can do is get as close as I can and see where I'm at. It doesn't make sense on their part at this point to rush to get [me] into a game or two or three. We'll see what happens."
Brian McTaggart is reporter for MLB.com and writes an MLBlog, Tag's Lines. Follow @brianmctaggart on Twitter. This story was not subject to the approval of Major League Baseball or its clubs.