Myers sustained an upper-body injury Friday in a 4-2 road loss to the Carolina Hurricanes. Defenseman Alexander Sulzer also was injured following a hit from Jiri Tlusty and will be out at least a week.
Ristolainen was the Sabres' first-round selection (No. 8) in the 2013 NHL Draft. It will be his first NHL action since Nov. 16.
The 19-year-old started the season in Buffalo, with one goal and a minus-4 rating in 19 games before being sent to Rochester, where he had six goals and 18 points in 30 games.
"I'm sure Rasmus thought he was capable of playing at this level at that time, and rightfully so," Sabres coach Ted Nolan said after the morning skate. "There's nothing like some good tutelage and development to make you a good player."
The Sabres will start goalie Jhonas Enroth against the Islanders, spelling recent acquisition Michal Neuvirth, who has stopped 93 of 98 shots in two losses since coming in a trade from the Washington Capitals.
"Since the Ryan Miller trade, these two young kids were given an opportunity and they're both battling for an opportunity, which is great," Nolan said. "There's nothing like internal competition to get the best out of any athlete."
Another young goalie, Anders Nilsson, will start for the New York Islanders, who held an optional skate after losing 4-3 Friday to the San Jose Sharks. Defenseman Matt Carkner will replace Matt Donovan in the lineup.
Here are the projected lineups for the Sabres and Islanders: