According to reports it's a crucial scene in the film that comes just before the interval and John will be seen banging his head on a glass table.
Reportedly the director of the film Anees Bazmee asked John to take a break and offered to postpone the shoot but John decided to cover his bruises with makeup and completed the scene. It was last scene before pack up so he wanted to complete it. John joked about his injury that he ended up injuring himself shooting for a comedy film more than shooting for a action film.
This is not the first time John has hurt himself on the sets of Welcome Back. Earlier he had a neck sprain while riding a Hummer in the deserts of Dubai.
The film is being directed by Anees Bazmee and being produced by Sajid Nadiadwala. It stars John Abraham and Shruti Hassan in the lead role.