He was expected to be a big part of the rebuilding process the Blackhawks are undertaking this season as they transition to younger players in key positions. Instead, Toews will not attend training camp and there's no timetable for his return.
"This offseason, I've been experiencing symptoms that have left me feeling drained and lethargic," Toews said in a statement Tuesday. "I am working with doctors so I can better understand my condition."
For the Blackhawks, already without center Kirby Dach for 4-5 months following wrist surgery and restricted free agent center Dylan Strome, who remains unsigned, it's more than losing another player at the position. It's losing someone who helped re-establish a winning culture in Chicago and could pass those lessons along to a new generation.
Blackhawks general manager Stan Bowman said they planned to lean heavily on Toews and forward Patrick Kane to set an example for future leaders, including Dach and defenseman Adam Boqvist.
"They could be a big help there, because they've lived that life not that long ago, where they've transitioned from being a hot-shot young player to being the guy who the other team is focused on, and it's not easy," Bowman said in October. "You get the other teams' best players paying attention to you, and harder matchups. So I think they can explain to those young players that there are going to be some ups and downs and you have to try to work your way through it. I think one of the benefits is to be able to guide them along, show them how you dealt with it when you were getting more attention. What are some of the things you would focus on to maintain your confidence and not get too frustrated?"
Toews, the No. 3 pick in the 2006 NHL Draft, arrived in the NHL in the 2007-08 season. In the previous 10 seasons, Chicago made the Stanley Cup Playoffs twice and failed to advance past the first round.
It also missed the playoffs during Toews' rookie season but quickly evolved into a model NHL franchise. During a seven-season stretch from 2008-15, the Blackhawks reached the Western Conference Final five times and won the Stanley Cup in 2010, 2013 and 2015.
Toews fingerprints were all over the rise to prominence and remain today. They are evident in little gestures of gratitude to teammates to the culture he passes along to prospects.
Jamal Mayers, who played for the Blackhawks from 2011-13, said he remembers Toews always having a sixth sense about what teammates needed.
"This is going back years when I was with him, but he had, even at a young age, when he was in his mid-20s, he had an uncanny ability to have the pulse of the whole room, in the sense that some guys needed a hug, some guys needed a kick in the butt," said Mayers, who retired after the 2012-13 season. "He had a great understanding of where everyone was in order to get everyone on the same page. That's probably the most impressive thing for me, seeing him as a younger player, being able to see that."
It's common to see Toews working on face-off skills after practice with younger centers. With a 56.9 percent face-off winning percentage for his NHL career, Toews doesn't need the extra work, but passing on tricks of the trade is part of his leadership.
"He used a lot of skill and homework and video and watching different players to beat those players," former Blackhawks forward Bryan Bickell said. "He's a leader in the room. The way he works in the gym, the way he prepares, he gets his mind, body, everything ready for each game. That's the player you build a franchise around and that's what the Blackhawks did. Hopefully he can bounce back and get the season rolling."
Toews scored 60 points (18 goals, 42 assists) in 70 games last season, second on the Blackhawks to Kane, who scored 84 points (33 goals, 51 assists) in 70 games. Toews scored nine points (five goals, four assists) in nine postseason games, tied with Kane for the Chicago lead.
When the Blackhawks open training camp Jan. 3, they'll look much different from the team that upset the Edmonton Oilers in four games in the best-of-5 Stanley Cup Qualifiers before losing to the Vegas Golden Knights in five games in the Western Conference First Round.