In trading their top scorer to the New York Islanders, the Sabres agreed to pick up 19.5 percent of what's left of the $6.4 million Vanek is still owed in the final year of his contract, a person familiar with the deal confirmed to The Associated Press on Tuesday.
The person spoke on the condition of anonymity because neither team revealed this detail as being part of the trade on Sunday.
Canadian-based SportsNet.ca first reported Buffalo was picking up part of Vanek's salary earlier in the day.
In exchange for Vanek, the Sabres acquired forward Matt Moulson and two draft picks: a first-round selection in June and a second-rounder in 2015.
Vanek is set to make his Islanders debut Tuesday night, when his new team hosts the New York Rangers.
Vanek is in the final year of a seven-year, $50 million contract Buffalo matched after Edmonton signed him to an offer sheet in July 2007. He's a two-time 40-goal-scorer, and eligible to become an unrestricted free agent after this season.
Moulson's addition has already begun paying off. He scored twice in a 4-3 loss to Dallas on Monday.
A three-time 30-goal-scorer, Moulson is also in the final year of his contract and faces the possibility of being traded once again this season. It's unclear whether he fits in Buffalo's long-term plans.
The Sabres (2-11-1), who have matched their worst start to a season through 14 games, are in the midst of rebuilding through the draft and developing their young prospects.
Buffalo is off until Thursday, when it visits the Rangers.