Allen suffered the injury on an incredible near-touchdown grab. He returned for one play, but quickly left the field and was taken to the locker room before halftime.
The wideout returned to the sidelines for the start of the third quarter, but didn't re-enter the game.
Chargers head coach Anthony Lynn said after the game that Allen will undergo further evaluation, but provided no update on the severity of the injury, according to Eric Williams of ESPN.
Allen failed to record a catch before exiting.