Scotland lock Jonny Gray is "unlikely" to make the World Cup after dislocating his knee last month, according to head coach Gregor Townsend.
The 29-year-old, capped 77 times, is not included in Townsend's initial training squad.
Winger Darcy Graham, back-row Rory Darge and hooker Stuart McInally return after missing the Six Nations.
Second row Cameron Henderson and centre Stafford McDowall are the only uncapped players in the 41-man group.
Townsend, who has just signed a new contract running to April 2026, must trim the squad to 33 for the tournament in France this autumn.
Scotland are in World Cup Pool B, along with defending champions South Africa and Six Nations winners Ireland.
Tonga and Romania make up the group, with matches played between 10 September and 7 October.
Scotland will play warm-up games against Italy, France and Georgia in Edinburgh over the summer and will meet France again away from home.
"The cohesion of the Six Nations really helped us improve as a squad," said Townsend. "That's going to be really important and exciting over the next few months as we get to work with the players for three - four months, which only happens once every four years.
"We could easily have picked a bigger squad. That would have been the easy thing to do but we feel the right thing is to keep it as tight as possible to build that cohesion.
"Certain positions required a lot of debate over the last few weeks. It shows the depth we have to leave out some quality players.
"I was really keen for 38, but then there was Jonny's injury and a couple of other things. My goal is to get the squad down to 33 pretty quickly, maybe after the second warm-up game."
Hooker Fraser Brown, who made four appearances as a replacement in this year's Six Nations, is omitted, along with centre Mark Bennett and former England winger Ruaridh McConnochie, who was in the Six Nations squad but did not feature.
On losing Exeter's Gray, Townsend said: "Would he become available at some point during the World Cup? Maybe. It's going to be at least four months until he is ready to play.
"It might be that he's back in full training and we pick up an injury a couple of weeks into the tournament, but I think it's unlikely where we are standing today."
Star full-back Stuart Hogg and another former captain, McInally, have already announced plans to retire after the World Cup.
Scotland failed to progress from the group stage four years ago, following defeats to Ireland and hosts Japan.
Scotland World Cup training squad
Forwards: Ewan Ashman, Jamie Bhatti, Dave Cherry, Andy Christie, Luke Crosbie, Scott Cummings, Rory Darge, Jack Dempsey, Matt Fagerson, Zander Fagerson, Grant Gilchrist, Richie Gray, Cameron Henderson, Stuart McInally, WP Nel, Jamie Ritchie (capt), Pierre Schoeman, Javan Sebastian, Sam Skinner, Rory Sutherland, George Turner, Murphy Walker, Hamish Watson.
Backs: Jamie Dobie, Darcy Graham, Chris Harris, Adam Hastings, Ben Healy, Stuart Hogg, George Horne, Huw Jones, Blair Kinghorn, Stafford McDowall, Ali Price, Cameron Redpath, Finn Russell, Ollie Smith, Kyle Steyn, Sione Tuipulotu, Duhan van der Merwe, Ben White.