Halak, 28, is set to become an unrestricted free agent July 1 and is expected to test the market.
According to a league source, it is almost certain that the Sabres will deal Halak in the coming days, with the Minnesota Wild and Washington Capitals believed to be in the mix.
Halak will not be starting for the Sabres in their game on Monday against the Dallas Stars.
Meanwhile, right wing Chris Stewart, acquired along with Halak from the Blues, could also be on the move.
While Stewart will play for Buffalo on Monday, barring a trade prior to the game, the Ottawa Senators have been on his trail and could work out a deal with the Sabres.
It's believed the Sabres are interested in Senators prospects Shane Prince and Mike Hoffman, among others.