Head coach Lindy Ruff feared after Tuesday night's 6-2 win over the Detroit Red Wings that Vanek would be out for "weeks" with what had only been described as an "upper body injury."
But that diagnosis apparently changed dramatically overnight.
"He came today a lot better. He may be available to play on the weekend," Ruff told ESPN.com on Wednesday. "Maybe not Friday, but Saturday. Although I'm not ruling him out for Friday, either."
That's potentially a huge break for the Sabres, who can ill afford to lose Vanek, a two-time 40-goal scorer, for a long period. Buffalo struggled last season with Vanek and goalie Ryan Miller both injured for long stretches.
Vanek's shoulder was not in a sling when he left the locker room after the game ended and he was believed to have had X-rays of his ribs, The Buffalo News reported Wednesday.
Vanek did not return after scoring his second goal of the game against Detroit at 12:46 of the second period.
Though Vanek fell awkwardly after snapping in the shot at the right post, Ruff said the player had been hurt earlier in the game. Vanek spent a few moments on the bench wincing in pain before leaving for the locker room.
"It was before the goal, when I collided with [former Sabres forward Brad] May," Vanek told The Buffalo News. "I went to hit him, and it happened there. I just finished the shift and felt it after. I knew right away and just tried to tough it out. After the shift, I just got it checked out."
Pierre LeBrun covers the NHL for ESPN.com. Information from The Associated Press was used in this report.