It"s because he"s afraid of being sidelined. The actor, who plays the protagonist in the film, has two scenes with south Indian actor, Sudeep (remember him from Phoonk?). And he feels that Sudeep is more prominent than he is in both the scenes. Like there is a scene where Vivek threatens Sudeep who only glares at him coldly and doesn"t respond.
Vivek feels the cold stare carried more impact than any dialogues and is now worried that Sudeep will be more noticed than him in the film.