Switzerland will have San Jose Sharks defenceman Mirco Mueller, who leads all rookies in blocked shots and will become a go-to guy in Group B play in Toronto.
"As an important young player to our franchise for now and the future, we think this experience will provide a positive impact on his career moving forward," Sharks general manager Doug Wilson said in a statement.
The Dallas Stars will let defenceman Julius Honka play for defending champion Finland, as long as they don't sustain any injuries in the next two games. Honka has spent the season with the AHL's Texas Stars.
Sweden and the Czech Republic are getting boosts as well. Philadelphia Flyers defensive prospect Robert Hagg will play for the Swedes, and Boston Bruins forward prospect David Pastrnak will return to play for the Czechs.
Hagg and Pastrnak, like Honka, have been in the AHL.
A handful of teams have been stingy with their junior eligible players. In some cases, like the Florida Panthers with blossoming No. 1 pick Aaron Ekblad, it has happened without much protest.
The Vancouver Canucks did not loan Bo Horvat to the Canadian team, which will instead have Lazar from the Ottawa Senators and Anthony Duclair from the New York Rangers in its lineup. The Senators announced Thursday that Lazar, who was their fourth-line centre, would be allowed to go.
Hockey Canada and the Senators had lengthy discussions about Lazar's role at the world juniors. Some of the Senators' questions are the same ones other clubs have about sending players to this tournament.
"With all the teams, there are a lot of questions they want to understand," said Scott Salmond, Hockey Canada's vice-president of hockey operations. "At the end of the day, it is their player, as much as I think they want to help us, they want to make sure they are getting a better player back. They understand what kind of role he is going to play, on and off the ice, when we would need him, all sorts of things.
"To make their decision, they need to have the information in regard to where we see him, how much we see him and what kind of role he is going to play."
The Edmonton Oilers decided to keep centre Leon Draisaitl rather than let him play for Germany. Draisaitl, the No. 3 pick in the 2014 draft, has averaged 12:42 of ice time as a rookie.
On Friday, the Washington Capitals sent 19-year-old forward Andre Burakovsky to the AHL's Hershey Bears after playing in 26 NHL games and putting up 13 points. Burakovsky was a point-a-game player at last year's tournament in his hometown of Malmo, Sweden.