As the offense continued to make mistakes throughout the day, boos reigned down from the Arrowhead stadium crowd as Cassel walked back out to the huddle.
His day would be cut short, however, as he sustained a head injury, opening the door for backup Brady Quinn.
But neither he nor the Ravens could find the end zone as Baltimore used three field goals to beat the Chiefs 9-6 on Sunday.
Cassel was sandwiched between two defenders on a screen pass to Dexter McCluster before dropping to the ground for over a minute. He walked off the field under his own power to the sound of cheers for Quinn.
Head Coach Romeo Crennel was not sure of Cassel's status immediately following the game. He said the quarterback would be evaluated early this week.
The Chiefs (1-4) offense was more conservative with Cassel than at any other point this season. He threw just six first quarter passes and completed 9 of 15 attempt on the day. He finished with 92 yards and two interceptions.
Those picks attributed to another tough outing in terms of ball possession. Kansas City committed four on the day, giving them 10 in their last two games.
That put pressure on a Chiefs defense that, otherwise, had it's best outing of the season against a highly-praised Ravens (4-1) offense. The unit held Baltimore to 298 yards and forced a pair of turnovers. Defensive lineman Tamba Hali and Justin Houston each picked up two sacks as well.
To balance Cassel's limited role, the Chiefs racked up 50 rushing attempts on the day. 30 of those went to Jamaal Charles, who finished with 140 yards after cracking the century mark in the first half. Shaun Draughn carried 12 times for 40 yards.
Two Baltimore field goals came after the Chiefs coughed up the ball, meaning Kansas City has surrendered 23 points off turnovers in the last two weeks. Kicker Justin Tucker's boots came from distances of 28, 26, and 39 yards.
Ryan Succop delivered all six Kansas City points, connecting on attempts of 30 and 31 yards away.
The Chiefs seemingly found the end zone on Quinn's lone drive late in the fourth. He marched the offense down the field, completing all three of his passes for 32 yards. He hooked up with Dwayne Bowe on a 15-yard scoring strike. However, it was waived off following an offensive pass interference penalty on McCluster.
Kansas City's offense accumulated 338 yards on the day, but failed to score a touchdown in a game for the second time this season.
The Chiefs head to Tampa next Sunday to face the Buccaneers.