"I haven't been able to help the team win," Ristolainen told Finnish outlet MTV Sports, according to The Buffalo News via Google Translate. "Recent seasons have been tough and I haven't been able to enjoy hockey."
Despite winning 10 games in a row and at one point sitting first in the NHL standings during the 2018-19 campaign, the Sabres missed the playoffs by a considerable margin for an eighth consecutive year.
Last season marked Ristolainen's sixth with Buffalo after the Sabres drafted him eighth overall in 2013. The 24-year-old produced 43 points in 78 games but was a league-worst minus-41.
The Sabres have had a busy offseason, including hiring Ralph Krueger as their new head coach and trading for Colin Miller. Before adding Miller, Buffalo also acquired Brandon Montour in a February trade with the Anaheim Ducks, which could make Ristolainen expendable as both newcomers play on the right side of the blue line.
Ristolainen reportedly drew interest in trade talks after the Winnipeg Jets dealt Jacob Trouba to the New York Rangers in June.