The crime happened Sunday night around 10:30 at the In-N-Out - at Martin Luther King Junior Way - near 15th Street in Merced.
When officers arrived, the suspects had already left. But witnesses say two people came inside, wearing ski masks.
The first suspect confronted customers inside, and the second walked up to the cash register and knocked it off the counter.
Witnesses say both suspects acted like they were armed, but one person could see that neither had a gun, so he confronted them.
One of the suspects hit the man in the face, giving him a black eye, and then, both ran from the restaurant.
Police say neither got away with any money.
Anyone with information about this attempted robbery is asked to call Merced police.