Tarasenko has 10 points (three goals, seven assists) in 10 games. His 33 goals led the Blues in 2018-19, and he scored 11 in the Stanley Cup Playoffs to help St. Louis win the Stanley Cup for the first time in its 51-season history.
The Blues (6-3-3) have won three of four entering their next game, at home against the Minnesota Wild on Wednesday (8 p.m. ET; NBCSN). They lost their first game without Tarasenko, 3-0 at the Boston Bruins on Saturday.
Tarasenko is one of five Blues with at least 10 points. Brayden Schenn leads them with 13 points (nine goals, four assists), O'Reilly and forward David Perron each has 12, and Jaden Schwartz has 10.
The Blues said Monday that Tarasenko will be re-evaluated five months after the surgery, meaning the earliest he would return is late March. They play their final four regular-season games March 29-April 4.
"We're going to need guys to keep stepping up, and obviously it's a great opportunity for young guys that will probably have better looks, better chances," Perron said Sunday. "That's what you crave for as a young guy, to have more ice time, better players to play with, things like that. We're looking forward to see what's going to happen and the guys that will step up in those roles."