The forward was injured when he fell awkwardly into the boards following a collision with Ottawa Senators defenseman Thomas Chabot after scoring at 6:55 of the third period during a 5-2 win at PPG Paints Arena on Monday. He went to the locker room holding his right arm and did not return.
The Penguins said Guentzel is expected to be sidelined for 4-6 months, putting his earliest return sometime in the Stanley Cup Playoffs should Pittsburgh qualify.
"It's tough," Penguins captain Sidney Crosby said. "To see him playing as well as he has been and he was taking his game to another level, you want to see your teammate succeed, especially a guy like that. Just found every way to contribute. To see that happen, it's an unlucky thing.
"He's as tough as they come, and I'm sure he'll make sure he's back as soon as possible. I don't think there's anything you can really say to someone in that situation. You feel for them."
Guentzel leads the Penguins in goals (20) and points (43), and was named Monday to the Metropolitan Division team for the 2020 Honda NHL All-Star Weekend.
"Things were going well for him," forward Bryan Rust said. "He was obviously having an unbelievable year, being kind of the catalyst behind our offense. Through everything, he's been kind of the one steady presence given the injuries. I think that's the reason he was our All-Star."
Pittsburgh is also without Crosby (core muscle surgery, 22 games missed), a center; forward Nick Bjugstad (core muscle surgery, 20 games); and defensemen Brian Dumoulin (ankle surgery, 12 games) and Justin Schultz (lower body, five games). Crosby skated with the Penguins at practice Tuesday for the first time since his Nov. 14 surgery, but there is no timetable for his return. He said he won't play when Pittsburgh hosts the San Jose Sharks on Thursday (7 p.m. ET; ATTSN-PT, NBCSCA, NHL.TV).
"He's not an easy guy to replace," coach Mike Sullivan said of Guentzel, "but we've lost some tough guys to replace here throughout the course of this whole season."
NHL.com independent correspondent Wes Crosby contributed to this report
