Muschamp said it was the same injury -- a radial tear of the meniscus in Morrison's right knee -- as running back Matt Jones, who required surgery.
"Very disappointed for him," Muschamp said.
Morrison is the 10th Florida player -- including seven who were listed as starters at the time -- lost for the season. The list includes Jones, quarterback Jeff Driskel, defensive tackle Dominique Easley, kick returner Andre Debose and offensive tackles Chaz Green and Tyler Moore.
Muschamp also said starting left tackle D.J. Humphries, who has missed two games with an MCL strain, is doubtful for Saturday's game at South Carolina. Starting quarterback Tyler Murphy (sore shoulder) and starting cornerback Marcus Roberson (ankle sprain) are expected to miss two days of practice but play on Saturday.
Morrison made headlines in the offseason when he was arrested twice within five weeks. He was arrested in Gainesville on June 16 for allegedly punching a bouncer. Morrison received deferred prosecution on the simple battery charge. He was jailed again July 20 and charged with barking at a police dog and resisting arrest. Both charges were dismissed a few days later.
Morrison was suspended for the first two games of the season. With a steady stream of injuries, Florida (4-5, 3-4 Southeastern Conference) has struggled throughout the season, especially in its ongoing four-game losing streak.
After losing 34-17 to Vanderbilt during its homecoming game, Muschamp said the team was "fragile" and had a "woe-is-me mentality" in regards to dealing with adversity.
"You just gotta coach through it," he said Monday. "We've just got to find ways to overcome that. It's something -- the psychological battle of getting our guys in the right situations so they can be successful.
"I certainly think [the amount of injuries] has had its effect. But we've got to find ways to get it right."