ST. LOUIS -- St. Louis Blues forward Patrik Berglund will have surgery on his right shoulder Friday and will be re-evaluated in four months.

Blues general manager Doug Armstrong confirmed Thursday that Berglund, who initially dislocated the shoulder at the end of the 2013-14 regular season, re-aggravated the injury while training this summer. He also said veteran center Scott Gomez has accepted an invitation to attend training camp on a professional tryout contract.

Berglund, 27, had 12 goals and 27 points in 77 games with the Blues last season and two goals and two assists in six games during the Stanley Cup Playoffs. Berglund has 118 goals and 247 points in 513 regular-season games, all with St. Louis, and six goals and 13 points in 29 playoff games.

"It's an injury we hoped we were past," Armstrong told NHL.com. "It happened a couple years ago entering the playoffs, and he did a great job of rehabbing and getting the strength back. We were hoping it was behind us, but he was training this summer [and] he aggravated the shoulder again. He came right to St. Louis when that happened and our trainers and [Berglund] worked on it, and it certainly wasn't going to get any better. So the surgery was necessary."

Berglund was taking part in a 4-on-4 scrimmage during informal workouts Monday when he collided with another player and left the ice in pain.

If the initial diagnosis holds, Berglund's return would put him in the lineup in January at the earliest.

Berglund initially injured his right shoulder April 11, 2014, during a game against the Dallas Stars. He was forced to miss three games, including the first two in the Blues' Western Conference First Round series against the Chicago Blackhawks.

He re-injured the shoulder Jan. 29, 2015, during a game against the Nashville Predators; he missed three games, returning against the Buffalo Sabres on Feb. 5.

The Blues already are without center Jori Lehtera, who had ankle surgery Aug. 4 and is out 6-8 weeks. Berglund's injury opens the door for Robby Fabbri, the 21st pick of the 2014 NHL Draft, as well as Gomez, 35, who had seven goals and 27 assists in 58 games with the New Jersey Devils in 2014-15 after he accepted a tryout and made the roster out of camp.

Gomez has 180 goals and 747 points in 1,045 games with the Devils, New York Rangers, Montreal Canadiens, San Jose Sharks and Florida Panthers. He had career highs in goals (33) and points (84) with the Devils in 2005-06. Gomez has 29 goals and 101 points in 149 playoff games and won the Stanley Cup twice with the Devils.

"It gives him a great opportunity," Armstrong said of Gomez. "I talked to Scott's representative when Lehtera went down. Seeing as Lehtera wasn't going to be participating in the first part of camp, if [Gomez] wanted to come in and play with some good players and show what he can do. Obviously now with the Berglund injury, it has opened up wide open for Gomez and for players like [Jordan] Caron and [Danny] Kristo and [Justin] Hodgman and obviously our own players like [Ty] Rattie, Fabbri, [Ivan] Barbashev. It's going to be a really competitive camp. The one spot that was locked down is now open."

Fabbri, who impressed in his first training camp last season, was someone the Blues were looking at potentially getting a nine-game NHL trial before deciding whether to keep him or return him to his junior team. The window just grew bigger for the native of Mississauga, Ontario.

"I can't answer that. Only Robby can," Armstrong said. "He's going to have to come in and have a great camp, as all those guys are, because this is a business now and all these players are training all summer to take advantage of an opportunity. Robby's not going to be given any more but certainly no less opportunity than Ty Rattie or Barbashev or a Caron for that matter, or a Gomez.

"We're in the winning business and I want these guys to come in and the first day of training camp show [coach] Ken Hitchcock and show myself and the rest of the organization that they're strongly competitive going for a spot on our roster."