Stevens, New Jersey's captain, confirmed Saturday he has post-concussion syndrome and will be sidelined indefinitely. Stevens missed his fifth straight game Saturday, when the Devils beat the Washington Capitals 2-1 in overtime.
New Jersey initially reported Stevens had the flu, but published reports suggested the problem was more serious.
The 39-year-old defenseman hasn't played since Jan. 7.
"I'm just resting and not doing anything at all," Stevens said. "It's really difficult. I'm used to being active, especially this time of year. I need to step back and rest."
Stevens has no idea when the concussion occurred and did not set a timetable for his return.
Stevens, voted to start for the Eastern Conference in next month's All-Star game, hadn't missed a regular-season game due to injury or illness since the 1999-00 season, when he sat out with the flu.
The absence of Stevens takes the emotional leader away from the struggling Devils, who had been 2-5-2 in nine games before beating Washington on Saturday.
"I like the four-on-four," said Elias, who had both of New Jersey's goals. "It's very exciting for the fans. You're trying to win a hockey game and it's been working for us."
In their last 10 outings, the Devils are 2-0-2 when the game has gone to overtime, compared to a 1-5-0 mark when it doesn't.
Pittsburgh, lingering at the bottom of the Atlantic Division, fell 4-3 to the Capitals on Saturday for its third straight loss. Milan Kraft and Konstantin Koltsov had power-play goals for the Penguins, who have scored with the man advantage in four consecutive games.
"That's the way our special teams have been all year," Pittsburgh coach Eddie Olczyk said. "When our power play is going well, our penalty kill lets us down."
The Penguins sent goaltender Sebastien Caron to AHL club Wilkes-Barre/Scranton on Monday. Caron, a dismal 5-17-3 this season with a 3.87 goals-against average, lost his roster spot to Jean-Sebastien Aubin.
Aubin was called up from the AHL when rookie Marc-Andre Fleury went to play for the Canadian junior national team last month. Aubin is 2-3 with a 2.28 GAA for the Penguins during Fleury's absence.
Fleury returned to the Penguins last week after leading the Canadian team to a silver medal.
This is a matchup of the league's best and worst defenses. The Devils have allowed just 82 goals, while the Penguins have yielded 169.