He died suddenly after undergoing knee surgery, two days after a game against the Buffalo Bills in 1965.

He gained 627 yards, second-most on the team, in 1965, even though he did not complete the season, dying in knee surgery after the 12th game.

[2] He was still on the operating table when his temperature suddenly spiked to 108 °F (42 °C), triggering severe convulsions, and he died 1+1⁄2 hours after surgery.

"[2][3][4] Team doctor Albert R. Miller said the embolism could have been caused by a fat globule breaking off and entering the bloodstream, or it could have been triggered by a severe reaction to the anesthesia.

[3] Head coach Hank Stram said, "Mack Lee Hill was a fine gentleman and a great football player.