The 31-year-old forward was placed on injured reserve after he left during the second period of a 4-2 win against the Ottawa Senators on Saturday.
"You just hope for the best result here as quick as possible. It's all you can really do right now," Sabres coach Ralph Krueger said. "It's one of those injuries where you need to have patience. It's definitely the inactivity that goes with it is always tough psychologically. But we're there for him. We're going to fix this together."
Okposo has missed time each of the previous three seasons because of concussions, including the final six games in 2016-17, his first with the Sabres after signing a seven-year contract July 1, 2016.
"First and foremost, he's a person, right? You think about him and his well-being; hockey comes second to everyone in this room as far as health-wise," defenseman Zach Bogosian said. "You think about him, you're gonna be there for him and be there for his family as well. Obviously going through what he's been through in his career, it's been tough for him so we're going to be there for him."
In 767 regular-season games with the Sabres and New York Islanders, who selected him in the first round (No. 7) of the 2006 NHL Draft, Okposo has 492 points (188 goals, 304 assists). He has 15 points (seven goals, eight assists) in 24 Stanley Cup Playoff games.
Forward Tage Thompson, who had been recalled from Rochester of the American Hockey League to replace Okposo, will miss 3-5 weeks because of an upper-body injury sustained during a 4-1 loss to the Chicago Blackhawks on Sunday.
Because Rochester also has several players injured, Krueger said he's unsure what Buffalo's lineup will look like Tuesday when the Sabres host the Minnesota Wild at KeyBank Center (7 p.m. ET; MSG-B, FS-N, FS-WI, NHL.TV). The coach did say Buffalo could dress 11 forwards and seven defensemen.
Injured forwards Marcus Johansson and Johan Larsson will not play Tuesday. Johansson, who is on injured reserve, has missed three games because of an upper-body injury; Larsson (upper body) has been out the past two.
"Just seems there's been guys going down at one moment, which is unfortunate," Sabres forward Sam Reinhart said. "I think the toughest thing is trying not to do too much. Our depth is going to really show for us, with guys in the minors and so forth. There's been some good play from guys coming up and we're just going to need to do it by committee and not rely on one or two guys like we kind of have the last few games, with [center Jack Eichel] scoring all the goals. Everyone's got to chip in that little bit extra and it's a fine line of not trying to do too much as well."
NHL.com independent correspondent Heather Engel contributed to this report
