A veteran Edmonton bus driver who was attacked by a passenger on his bus last December has severe brain damage and has permanently lost vision in his left eye, his doctor said Tuesday.

Dr. Julianna Nagy testified at a sentencing hearing that Tom Bregg suffers from poor depth perception, memory loss, balance problems and trouble sleeping.

Edmonton Transit driver Tom Bregg leaves the courthouse on May 6. (CBC)Bregg, 58, was repeatedly kicked and stomped on the face by Gary Edwin Mattson during the morning rush hour on Dec. 3.

Mattson punched Bregg and pulled him out of his seat after refusing to pay his bus fare. He then dragged Bregg onto the sidewalk and stomped on his face 15 times.

The attack was recorded by an on-board security video system.

Nagy also testified that Bregg's right eye is damaged.

The bus driver has lost his driver's licence because of his injuries. There's no indication he'll ever be able to return to work, the court heard.

Gary Mattson is shown on a security video moments before he attacked Edmonton bus driver Tom Bregg. (Alberta Justice)Mattson, 25, pleaded guilty earlier this month to aggravated assault and assaulting a peace officer.

Stu Litwinowich, president of Local 569 of the Amalgamated Transit Union, spoke outside the courthouse, describing Bregg as a "fighter." He said the union will do what it can to help the 33-year veteran of the transit industry.

"There's some opportunity in accommodating him into a different position within the city," Litwinowich said. "But all of that's up in the air right now until we see what happens with Tom. I know it's a long road yet."

Litwinowich said he fears Bregg may never drive again.

The sentence hearing will resume June 18 with Bregg delivering a victim-impact statement. The Crown has indicated it is seeking to have the court designate Mattson as a dangerous offender.