Smith, the 2006 Heisman Trophy winner, has been fighting a blood clot in his neck, which led to an infection in his lung. He has not practiced with the Ravens since Aug. 22.
Dr. Andrew Tucker, the Ravens' head team physician, said Monday that Smith's illness was "extraordinarily unlucky."
"It's a rare complication of a very severe tonsilar infection. Ironically, this type of problem, although rare, does happen most commonly in young, healthy people like Troy," Tucker said, according to the Carroll County (Md.) Times. "Troy is someone who's young, who's healthy, has a normal immune system, normal heart and lungs. Troy's health was never in danger. He was never critically ill."
Smith had been expected to compete for the starting position with Kyle Boller and rookie Joe Flacco, but Smith's illness and Boller's season-ending shoulder injury during the preseason elevated Flacco into a starting role.
Smith is taking antibiotics and is expected to make a full recovery. It's been recommended that he have his tonsils removed, but Tucker said that will likely happen in the offseason.
The Ravens do not expect to place Smith on the injured reserve list, a move which would end his season.
"We're pretty certain that he's going to be back playing for the bulk of the season," coach John Harbaugh said, according to The Baltimore Sun.
But it is not yet clear whether Smith will return as the backup to Flacco or get another chance to compete for the starting job.
"We think he's a heck of a quarterback, and he's going to make our team stronger when he comes back," Harbaugh said, according to The Sun. "[The decision] is going to be partly medical and football strategy -- what role can he play to help us win, where Joe is at and where the offense is at. I know one thing: When he comes back, it's going to be a big plus for us."