The incident was reported just before 7 p.m. at Fountain Avenue and Vine Street.
Police say two men got into a fight in the restaurant's parking lot. One stabbed the other multiple times and ran off.
The victim stumbled inside the El Pollo Loco and collapsed. Restaurant workers called 911.
The victim was rushed to the hospital in critical condition.
The suspect remains on the loose. A description has not yet been released.