Garrard, who had been largely ineffective, was replaced by Trent Edwards.
Team officials said after halftime that Garrard sustained a concussion and he did not return. The Jaguars lost 30-3.
"Losing David definitely hurt," wide receiver Tiquan Underwood said. "That's our quarterback, our captain, our leader."
Edwards, the former Buffalo starter who was claimed off waivers three weeks ago, finished 11 of 20 for 115 yards, with two interceptions.
"We never got any offensive rhythm," tight end Marcedes Lewis said. "To have Dave go out like that, everybody felt they had to press."
Witherspoon said Garrard looked bad after the hit, but said it was a clean knock on the quarterback.
"He definitely didn't look good," Witherspoon said. "I saw him wincing on the ground, but that's the nature of the game. It was a clean, solid hit."
Titans quarterback Vince Young sprained his left knee in the first quarter.
Information from The Associated Press contributed to this report.