Tkachuk has not skated since Monday, when he tested the injury but still experienced soreness in his midsection.
"It's a tough injury to deal with," Tkachuk told The St. Louis Post-Dispatch on Thursday. "Everything revolves around that part of the body. You're using it quite a lot. Hopefully I'll get better in a couple of days and be ready to go Monday or Tuesday."
Tkachuk will be out at least through Saturday, and he might return for Tuesday's game at Phoenix at the earliest.