The free-agent frenzy was in full swing when the NHL opened its doors for signings Monday afternoon, but the cap-strapped Flyers were relatively quiet, though they did restock their top minor-league affiliate.

The Flyers signed eight free agents who figure to help the AHL’s Lehigh Valley Phantoms: defensemen Nate Prosser, Andy Welinski, Tyler Wotherspoon, and Chris Bigras; center Kyle Criscuolo, a South Jersey native; left winger Andy Andreoff; right winger Kurtis Gabriel; and goalie Jean-Francois Berube.

“Several of these players will probably move back and forth between Philadelphia and Lehigh Valley,” general manager Chuck Fletcher said, adding he wanted to add veterans to surround the youngsters who are starting their pro careers with the Phantoms.

Fletcher, who said the majority of the players signed were upgrades compared with what the Phantoms had last season, is extremely familiar with Prosser, Gabriel, Welinski, and Criscuolo from his nine years as the Minnesota Wild’s GM.

Prosser spent parts of 11 seasons with the Wild, Gabriel was drafted by Fletcher (third round) in 2013, and the right-handed Welinski, who got into 26 NHL games with Anaheim last season, played four years at the University of Minnesota-Duluth.

Criscuolo was an intern for the Wild who worked in the analytics department when Fletcher was there.

The Flyers’ cap situation is in flux because they still need to sign restricted free agents Ivan Provorov, Travis Konecny, and Scott Laughton.

If those three players signed for, say, a combined $13 million annual cap hit, the Flyers would have only about $2.7 million of cap space remaining.

Of the unrestricted free agents who signed Monday, only a few players who could fill the Flyers’ needs would have fit under their projected cap, including right winger Corey Perry, who signed a one-year contract with Dallas for $1.5 million, with a chance to make an addition $1.75 million in incentives; and right winger Alex Chiasson, who re-signed with Edmonton for two years with an annual $2.15 million cap hit. Chiasson, 28, had 22 goals last season.

“We didn’t jump into those waters,” said Fletcher, who doesn’t expect to make any major moves before training camp, but he said that some teams are over the cap and that some trade opportunities might arise.

Fletcher noted that the Flyers have several prospects getting close to the NHL, “and I don’t think it’s a very smart thing to box these kids out and take on additional cap responsibilities."

Prosser, 33, a right-handed defenseman, spent most of last season in the AHL. The 6-foot-2, 201-pound Prosser got a one-year, two-way contract ($700,000).

Andreoff, Criscuolo, and Gabriel were brought in to beef up the Phantoms’ forward depth.

Andreoff had 26 goals with Syracuse (AHL) last season, and Criscuolo, a 5-8, 170-pound native of Southampton, N.J., who once played at St. Joseph’s Prep, had 20 points in 43 games during an injury-plagued season with Rochester.

Gabriel had two goals in 22 games with the New Jersey Devils last season and was suspended one game for boarding Nolan Patrick in a March 1 loss to the Flyers.

Bigras, 24, drafted in the second round (32nd overall) by Colorado in 2013, appeared in 52 AHL games last season for Hartford. He has played in 46 NHL games with the Avalanche.

Berube, who will turn 28 on July 13, had a 3.01 GAA and .896 save percentage for the AHL’s Cleveland Monsters last season. He has played in a total of 34 NHL games with Chicago and the Islanders, compiling a 3.39 GAA and .898 save percentage.

None of the Flyers’ moves shook up the NHL, like the Rangers’ signing of Artemi Panarin, the Predators’ signing of Matt Duchene or the Panthers’ signing of Sergei Bobrovsky.

The Flyers, who made three major moves last month — including the signing of Kevin Hayes, who would have been one of the top centers on the market if he had become an unrestricted free agent Monday — weren’t able to sign a right winger to fill their opening on the third line. (Gabriel, a 6-4, 200-pounder, is a long shot.)

That’s good news for promising prospects Morgan Frost and Joel Farabee, who will be among the players battling for that spot in training camp. Laughton could also be in the running, and the Flyers still might sign a (cheap) free agent in the next couple of months or make a deal.

Frost, a natural center, and Farabee, a natural left winger, both say they could play right wing. Both say their goal is to make the team out of training camp.

Fletcher is keeping an open mind. He thinks those two, along with German Rubtsov, Isaac Ratcliffe, Mikhail Vorobyev, Andreoff, and Gabriel will compete for roster spots.

“That’s what training camp is for," he said. “It’s an opportunity for players to show they belong. It should be an exciting camp.”

Last week, Fletcher said that ideally he would like his young prospects to get some seasoning with the Phantoms, but that it was “the most talent I’ve seen in a development camp” since his front-office career started in 1993.

Among Monday’s signings: Former Flyer Wayne Simmonds, a hard-nosed right winger who struggled after being traded to Nashville last season, received a one-year, $5 million deal from New Jersey. He will oppose the Flyers when they play their home opener Oct. 9.

Breakaways

The Phantoms lost Mike Vecchione to St. Louis and Tyrell Goulbourne to Vegas in free agency. ... Former Flyers and Kings coach John Stevens was hired as an assistant in Dallas, which is directed by former Flyer Jim Montgomery. … Former Flyer Luke Schenn signed with Tampa Bay, his seventh team in the last nine years. ... Ryan Hartman, another ex-Flyer, got a two-year deal from Minnesota with an annual $1.9 million cap hit.