The Czech team announced the move after the Bruins were eliminated from the NHL playoffs in a second-round series loss to the Tampa Bay Lightning.
The offensive duo will no doubt improve the Czech firepower at the tournament in Denmark. The Czechs face next Russia on Thursday.
The 21-year-old Pastrnak had 20 points in 12 playoffs game for six goals and 14 assists after he finished the regular season with 35 goals and 45 assists for 80 points.
Krejci scored three and added seven assists in the playoffs. He had 44 regular season points for 17 goals and 27 assists.