PHILADELPHIA (CBS) — The mystery behind Flyers center Nolan Patrick’s upper-body injury has been solved. The Flyers on Thursday announced that the 2017 No. 2 overall pick will miss the start of the season because of a migraine disorder.

Patrick is considered “week-to-week,” according to Flyers general manager Chuck Fletcher.

“Patrick will not be going to Europe and we will provide additional information once the team returns,” Fletcher said in a statement.

The 21-year-old has been with the Flyers throughout training camp, working out on the ice by himself and attending team meetings but hasn’t been able to play.

Injuries so far have held Patrick back in his young hockey career, even before the Flyers drafted him in 2017. He suffered a sports hernia in 2016 while playing for the Brandon Wheat Kings in 2016 and then had complications from that injury during his draft year in 2017.

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In his rookie season in 2017-18, Patrick missed nine games with a concussion and he also suffered a concussion last season.

Last season, Patrick scored 13 goals and 31 points in 72 games but didn’t take the step forward the Flyers’ front office expected him to take.

As a result, Fletcher traded for and then signed center Kevin Hayes to a seven-year, $50 million contract during the summer to be the team’s second-line center. Patrick’s migraine disorder immediately makes the Hayes signing even more important.

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With Patrick out, the Flyers have a few options to fill out their bottom six.

The most likely scenario will be Scott Laughton sliding into the third-line center role with Connor Bunnaman serving as the team’s fourth-line center.

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Claude Giroux and Michael Raffl have both played center in the past, though all indications point to the Flyers wanting Giroux to stay at left wing this season. Raffl is another candidate to play center.

The early favorite to start the season would be Laughton at 3C, Bunnaman at 4C with Joel Farabee, Carsen Twarynski and Chris Stewart battling it out for the open bottom-six wing opening.

Tyler Pitlick, who’s recovering from a wrist injury, is nearing a return too. It’s unclear if he’ll be ready for the start of the season.

The Flyers head to Europe after Thursday’s preseason game against the New York Rangers. They face off against Lausanne HC in the final preseason game on Monday and then open the 2019-20 season against the Chicago Blackhawks in the NHL Global Series next Friday.