Tyquan Thornton suffered a dislocated left ankle in Week 4 (October 4) against the Raiders — a gruesome injury where his foot was facing the wrong direction after a 55-yard TD catch. He had surgery, and the recovery timeline is about 3–4 months.
Per the wiki (from the Tyquan Thornton page), there's a "small chance" of a late-season return, but it's more realistic that he's out through November at minimum and possibly into the playoffs. So a return this season isn't impossible, but it's unlikely unless the Chiefs make a deep playoff run and he heals on the faster end of that window.