The Gators' medical staff diagnosed Johnson with congenital cervical stenosis, a condition affecting the spinal cord.
Johnson suffered an injury during a scrimmage on April 3 that caused him to feel numbness in his fingers.
The 6'6'', 296-pound redshirt sophomore missed the final week of camp, and on Saturday Florida coach Jim McElwain said Johnson's prognosis "doesn't look great."
Johnson was projected to start on the Gators' line this season after making three starts and appearing in all 12 games last season.
Florida had only six scholarship offensive linemen able to participate in the spring game.
4/3/15 will tat it on me my last play in the swamp saw that white light when I went down and I stood and walk off the field with pride— Rod Johnson #⃣5⃣5⃣ (@Almighty_rod55) April 14, 2015