Forwards Nathan Walker and Mackenzie MacEachern, defenseman Calle Rosen and goaltender Malcolm Subban went unclaimed by the other 31 teams and were assigned to the minors before Monday’s roster deadline of 4 p.m.

Rosen was probably the likeliest to get claimed, given his strong results last season and his cheap cap hit, but instead will stick in the Blues organization as a depth defenseman in case of injuries on the blue line.

The Blues kept eight defensemen on their NHL roster, as Scott Perunovich, Tyler Tucker and Robert Bortuzzo remained in St. Louis. What made Rosen the odd man out on defense?

“I don’t think it’s one thing or another,” Blues coach Craig Berube said after practice Monday morning. “I think Perun showed us this year that he’s taken another step. He’s got some pretty good ability, Perun, offensively. We felt that he did enough in camp and throughout camp, it got better and better as it went along. Decisions have to be made.”

Rosen, 29, had eight goals and 10 assists last year in 49 NHL games and also had a team-best plus-19 rating.

Walker and MacEachern were beat out for the final spots up front by Jake Neighbours, who will be on the fourth line, and Nikita Alexandrov, who will serve as the 13th forward to begin the season.

Alexandrov solidified his spot on the roster with a couple of strong showings in the last two preseason games in Dallas and against Chicago.

“We were waiting for him to show us what he’s capable of doing, and I thought he did that the last two games,” Berube said.

Neighbours, meanwhile, improved in his last two games of the preseason, with goals against the Stars and Blackhawks after opening the preseason with zero shots on goal in his first two games. Berube said the Blues want Neighbours to become a quicker player.

“Jake Neighbours is coming,” Berube said. “He’s working, he’s coming. His camp has gotten better as it’s gone along here. He still has to keep working and keep pounding away at things. It’s all about becoming a real good pro for him, and he’s getting close. ... He gets to the hard areas of the ice all the time, whether it’s on the forecheck, whether it’s around the net. He’s heavy on pucks. I think he’s got a good head for the game.”

In clearing waivers and being loaned to Springfield, Subban will join Vadim Zherenko as the Blues’ goaltending tandem in the AHL. Subban, 29, has played 86 career NHL games.

Defensemen Josh Jacobs (knee) and Anton Malmstrom (shoulder) were not on the ice at all during training camp, and were designated injured/non-roster. They will carry a cap hit of $0 on the Blues cap.

The Blues announced Monday morning that the team would be hosting the Tom Kurvers Prospect Showcase next year in mid-September the weekend before training camp begins for the 2024-25 season. It will take place at Centene Community Ice Center.

The showcase will also feature Chicago and Minnesota, as each team will play two games. The Blues played in the tournament for the first time last month in St. Paul, going 1-1-0. Previously, the Blues participated in the Traverse City Prospect Tournament but decided to switch this season.

The Tom Kurvers Prospect Showcase is easier on the players (who play two games instead of three or four), on the staff (who spend less time on the road), and on the wallets (as the Blues won’t even have to travel every third year).

Next year, the Blues’ prospect roster could include bigger names like Dalibor Dvorsky (playing professionally in Sweden) and Jimmy Snuggerud (playing in college at Minnesota).

The event is the latest one scheduled to be held at CCIC. Last week, the Blues announced that CCIC would host the ACHA championships in 2024, 2025, 2027 and 2028, with an option to host in 2026. The ACHA is a college hockey organization that competes below NCAA teams.

St. Louis is also trying to land the 2026 World Junior Championship, which would use both Enterprise Center and Centene Community Ice Center as host sites. USA Hockey is expected to award the tournament before the end of the calendar year.

• The Blues left St. Louis after practice Monday and will spend the next two days doing team bonding in Frisco before opening the season against the Stars on Thursday night.

“It’s just good to get away as a group, do some things together,” Berube said. “We’ve got everybody involved. It’s nice way to get off to the start of the season.”

• Former Blues captain Ryan O’Reilly was named an alternate captain in Nashville on Monday afternoon. O’Reilly will return to St. Louis as a Predator on Nov. 24 after signing a four-year contract with Nashville over the summer.