In 60 games entering Tuesday, Downie had four goals, 24 points, 106 penalty minutes, and a plus-3 rating.
"I feel good now, and I'm ready to go," he said. "I'm looking forward, not backwards here."
Rinaldo played on the third line the previous two games. He received a four-game suspension from the NHL for an illegal check against Buffalo on Sunday.
"He brings the skating element and the physical element, and he's hard on the forecheck," coach Craig Berube said of Rinaldo. "He's a loss, for sure. He's a good player for us, and we're definitely going to miss him."
Downie had said he was ready to play about a week ago, but Berube was cautious to put him back in the lineup.
"He definitely got a little more skating in. We would have liked to get even a little bit more in than he did, but with the loss of Zac, we need him," Berube said.
Left winger Tye McGinn also returned to the lineup, replacing Jay Rosehill.
McGinn, a healthy scratch the previous two games, was on a line with Vinny Lecavalier and Adam Hall.
The Flyers caught a break when talented Florida goalie Roberto Luongo, Tuesday's projected starter, suffered an upper-body injury during warm-ups and could not play.
Instead, Florida used Dan Ellis, who took shabby numbers into the game: a 5-10 record, a 3.54 goals-against average, and an .883 save percentage.
Former Flyer Scottie Upshall, who plays wing on Florida's second line, went into the game leading the Panthers with 36 points. . . . Florida center Scott Gomez, who had been playing on the top line, was a healthy scratch. . . . Rinaldo on his suspension: "It sucks; it's the last thing I wanted to happen."