Rookie Morgan Frost created a slew of scoring chances in two preseason games and was a strong contender to start the season as the Flyers’ third- or fourth-line center.

That was before general manager Chuck Fletcher announced Monday that Frost would be sidelined five to seven days because of a groin strain.

Frost missed the first two preseason games with what the Flyers called a minor groin injury. He played in the last two and fared well, though he didn’t finish any of his scoring chances.

Frost wasn’t going to play in Monday’s exhibition game in Boston, but the plan was for him to be in the lineup Thursday against the host New York Rangers, the Flyers’ last preseason matchup against an NHL team.

There is an opening at center because Nolan Patrick has an undisclosed upper-body injury and will likely miss the Oct. 4 opener against Chicago in Prague.

With Frost sidelined, center German Rubtsov’s chances of being on the opening-night roster increased, though he didn’t play well in Monday’s 4-3 overtime loss in Boston. Rubtsov was a first-round selection in the 2016 draft.

Rookies Mikhail “Misha” Vorobyev and Connor Bunnaman are also candidates to play center. Scott Laughton, penciled in as the fourth-line center when camp started, could center the third unit when the season starts.