Flyers general manager Ron Hextall told reporters Timonen was experiencing pain in his calf for the past few days and went to the hospital Monday, when the blood clots were discovered in his lower right leg and in both lungs.
Timonen, 39, is hoping to be discharged Wednesday, but is unable to travel for 2-3 weeks. He will head to Philadelphia after that for further evaluation.
"He was working out hard and he was getting ready for the season, and then this happened," Hextall said. "I think he was as shocked as anybody. I haven't talked to him yet. I've reached out to him twice. He's in a hospital and he did send me a text, though. He seemed very frustrated, but I think we're all very happy for Kimmo, [his wife] Johanna and his three children that he's doing fine."
This is the second time Timonen has been diagnosed with a blood clot; he developed one in his foot after blocking a shot against Montreal Canadiens defenseman Andrei Markov during the 2008 Stanley Cup Playoffs.
If Timonen is out long-term, the Flyers will have a hole on their blue line. Hextall moved to fill it Tuesday night by signing free-agent defenseman Michael Del Zotto to a one-year contract.
No matter how Del Zotto plays, Hextall said Timonen will be missed.
"There's no question it's a setback, there's no other way to explain it. But we'll adjust and we'll do what we can to make the team better," he said. "But absolutely, you can't take not only the player, but I think the experience and the calm and the poise and the respect that Kimmo has in the locker room, and say you didn't take a step back."
Timonen has spent the past seven seasons with Philadelphia. He had six goals and 29 assists and averaged 20:20 of ice time in 77 games last season.
Philadelphia still boasts Mark Streit, Luke Schenn, Braydon Coburn, Andrew MacDonald, Nicklas Grossmann and Nick Schultz on its blue line, as well as Del Zotto. The Flyers also have other internal options, including Shayne Gostisbehere and Oliver Lauridsen.
Philadelphia opens the 2014-15 season on Oct. 8 against the Boston Bruins at TD Garden. Whether they'll have Timonen in the lineup remains to be seen, but Hextall is more concerned with his defenseman's well-being.
"This could be a long-term thing and we have to prepare as an organization that it is a long-term thing," Hextall said. "Can he play next season? I don't have the answer to that. I do know that he's in stable condition, he's doing well. Word is that he's supposed to be discharged [Wednesday]. So I think first and foremost, we're worried about Kimmo Timonen the person, not the hockey player."
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