Lehtonen was injured in Sunday's game between Finland and the United States when Team USA forward Bobby Ryan was tripped and then slid into Lehtonen, who left the game and did not return.
Valley said the injury, which is not serious, will likely sideline Lehtonen for two to three weeks. He should be fine after that.
Lehtonen will not play for Finland for the rest of the World Championship, which enters the playoff round on Thursday.
Thursday’s World Championship games (quarterfinals)
Canada vs. Slovakia, 5:00 a.m.
Russia vs. Norway, 7:45 a.m.
USA vs. Finland, 10:30 a.m.
Sweden vs. Czech Republic, 1:15 p.m.