[Kansas City.com] The Chiefs said Matt Cassel had nothing more than the wind knocked out of him when he left their final preseason game against Green Bay midway through the second quarter after being sacked.

It turns out Cassel has more than that. Cassel has a rib injury that could prevent him from playing in Sunday’s regular season opener against Buffalo at Arrowhead Stadium.

If Cassel can’t play against the Bills, Tyler Palko is the likely starting quarterback. Palko has bounced around to several NFL teams but has never started a regular-season game.

A source close to the situation said Chiefs coach Todd Haley told Palko after the game, “You’d better be ready to play Sunday.’’

Cassel was injured when Green Bay’s 340-pound defensive lineman, Howard Green, landed on top of Cassel after the sack. Cassel got up in obvious pain after the play and immediately left the game in favor of Palko.

Cassel later did some throwing on the sideline as if he was going back in the game. He never did.