The Flyers young blue line is about to be tested without Sean Walker and Nick Seeler

SUNRISE, Fla. — And so it begins.

The Flyers’ toughest stretch of the season kicks off on Thursday night in the Sunshine State. First on the docket is a matchup against the top team in the NHL, the Panthers, on Thursday night. Saturday brings a meeting with the Tampa Bay Lightning.

And they’ll have to do it without four key defensemen.

» READ MORE: Trade grades: Evalutating the Sean Walker trade as Flyers net first-rounder in return

After much speculation, Sean Walker finally was traded. One-half of the Flyers’ most reliable pairing, the soon-to-be unrestricted free agent was shipped west to the Colorado Avalanche for a first-rounder and center Ryan Johansen.

That move was expected. But on the same day, the Flyers placed his partner Nick Seeler on injured reserve with a lower-body injury after he blocked a Colton Parayko screamer from the point with the outside of his left ankle. Losing either is tough. Losing both at the same time with the team already down blueliners Rasmus Ristolainen and Jamie Drysdale? Yikes.

The Flyers have just six healthy defensemen — so much for 11 and 7 — on the roster. Four have played the majority of the season with the big club — Cam York, Travis Sanheim, Marc Staal, and Egor Zamula. Ronnie Attard and Adam Ginning have entered the chat, and they have a combined zero games played this season. The 24-year-olds have just 18 NHL games between them with only one for Ginning. Gulp.

“It was just one game, but the thing I can take with me is that first game is done, and now I don’t have to think about that anymore, at least,” Ginning said Wednesday after being called up from Lehigh Valley.

All along, the Flyers have talked about playing their young defense, and now they will certainly have to. Staal, 37, is the elder statesman at more than 1,000 NHL games and Sanheim’s senior by 10 years. Sanheim entered Thursday with 478 career games to his name.

Now the kids will be thrown straight into the fire. A fire that is raging as the Flyers try to maintain their spot inside the playoff bubble now without Walker and their top shot blocker — and the top dog in the NHL with 184 — in Seeler.

“You’ve got some young kids on the back end now getting some time maybe in our next game here,” coach John Tortorella said Wednesday. “That’s the way we’ve got to look at it. You just fill it in, and, hopefully, Seels gets back as quickly as possible.”

It’ll be a tough task. The one positive for Ginning and Attard is that the Phantoms also have been playing meaningful games as they attempt to climb into the AHL playoff picture. Attard has 25 points (10 goals, 15 assists) in 46 games with Lehigh Valley this season, and Ginning has 13 points (two goals, 11 assists) in 52 games. They are up here because when Tortorella tasked general manager Danny Brière for reinforcements, the only directive was to call up who he felt was the best choice.

Now they’ll get a chance to prove it against some of the best in the NHL.

The Flyers may have acquired Johansen in the deal for Walker, but his tenure with the Flyers isn’t going to be a long one. Johansen was waived as soon as the phones were hung up to complete the deal on Wednesday, and he was assigned to Lehigh Valley on Thursday.

“Probably not,” Brière said when asked if Johansen is in the long-term plans. “We will see. We will see if we can give him a chance to go somewhere else. We haven’t decided what the future looks like for him yet.”

Brière wouldn’t expand much on the why, but he added that they are looking for a trade partner for Johansen and have asked him to “stand pat” for the next few days.

“We have a different vision at this point,” Brière said. “So that’s about all I can say. Maybe eventually I’ll be able to expand a little bit more, but still maybe we can find someone to take him at this point.”

Johansen has had an up-and-down career. This season he was expected to be the No. 2 center for the Avalanche after they acquired him from Nashville during the offseason. He never fit into their system and finished with 23 points (13 goals, 10 assists) in 63 games.

» READ MORE: Flyers defenseman Nick Seeler thrilled to call Philly ‘home’ with new contract extension

Travis Konecny returned to the lineup for the first time since Feb. 21 after sustaining an upper-body injury in practice two days later. He leads the team with 27 goals and 54 points and has missed the past six games... In case you went to bed early Wednesday, the Flyers played broker in the Noah Hanifan deal involving the Vegas Golden Knights and Calgary Flames. The Flyers will pay 25% of Hanifan’s salary for the remainder of the season which amounts to $1.24 million in return for Vegas’ 2024 fifth-round pick. They also traded Europe-based veteran Mikhail Vorobyev’s rights to Vegas in the deal. ... Acquired from the Ottawa Senators on Wednesday, Vladimir Tarasenko made his Panthers debut on Thursday. He has two goals and two assists in three games against the Flyers this season.