Chicago's Nate Robinson hit the first free throw to make it a three-point game with 10.6 seconds left and missed the second. That led to a jump ball, and a scramble for the loose ball ensued.
From the floor, the Bulls' Carlos Boozer threw it to Robinson. The ball went through the guard's hands and started to go into the back court. Robinson saved it to avoid the violation then missed a heave at the buzzer, but after the tip on the jump ball, Valanciunas' head hit Gay's shoulder.
Valanciunas fell backward and immediately grabbed the back of his neck. He was tended to for several minutes on the sideline and had his neck placed in a brace before being taken away on a gurney.
The Raptors said test results were pending late Tuesday and he would remain overnight at Chicago's Rush University Medical Center for observation.