The Miami Dolphins are signing backup quarterback Tyler Huntley off the Ravens' practice squad as Tua Tagovailoa remains out with the third diagnosed concussion of his pro career.

Multiple concussions increase the risks of long-term neurological issues and chronic traumatic encephalopathy (CTE), experts warn.

The 26-year-old left Thursday night's game after he leaned headfirst into a tackle and added to an already worrying history of brain injury, prompting fans and former players to urge his retirement.