Giroux stretched and fell to his knees trying to poke the puck away from Tampa's Ryan Shannon in the neutral zone with 2:08 left in the second. As Giroux went down, Simmonds was charging from behind and tried to leap over Giroux. But Simmonds didn't quite clear him, and his knee appeared to catch Giroux in the right side of the head.
Simmonds said the collision was unavoidable.
"He kind of fell and he was right in front of me," Simmonds said. "I was on the backcheck and I wanted to get into the play and I tried to jump over him. I don't know where I caught him."
Flyers General Manager Paul Holmgren said Giroux was evaluated by team doctors and held out for precautionary reasons. He added Giroux was not hospitalized and would be re-evaluated Sunday.
When asked if Giroux was suffering from any concussion-like symptoms, Holmgren said no.
"Not really a headache or anything like that," Holmgren said. "This is really just precautionary at this stage. We didn't want to put him back in there at that time. It's a game in December. Obviously he's one of our better players, so we'll err on the side of caution."
Giroux had two assists in the game, pushing his League-best points total to 39. He also leads the Flyers with 16 goals, 23 assists and five game-winning goals.
The news on Bryzgalov appears much less serious. Holmgren said a lower-body injury started bothering Bryzgalov during the second period -- and when Bryzgalov tried to play the third, the affected area began stiffening up, so the decision was made to remove him.
"After the second period he wanted to continue and it stiffened up on him in the third," Holmgren said. "We don't think it's anything serious. It's an off-day tomorrow (Sunday) for the players. I would assume he'll be fine for the next game (Tuesday in Washington).
Bryzgalov called the injury an "old boo-boo," and said he wasn't even day to day, more like "hour to hour."
"It started to get sore a little bit," he added. "It started bothering me more and more during the game. We decided to … be on the safe side."
Bryzgalov stopped 14 of the 16 shots he faced to win his fifth straight game.
With the Flyers already missing team captain and No. 1 defenseman Chris Pronger indefinitely with concussion-like symptoms, the absence of their best forward would be a huge blow.
"He's our best player," linemate Scott Hartnell said. "He's a big catalyst for us. He's so strong on pucks, he's great defensively. Obviously we know what he can do offensively. If he's out we're going to miss him big-time."