But actor Imran Khan, who plays a gangster in the latter, is unfazed and sees no point of competition.
Imran is not worried because he says films nowadays mint a major portion of moolah within the first weekend of release itself.
"Chennai Express" hits the screens Aug 9, "Once Upon A Time In Mumbai Dobaara!" releases Aug 15.
"They ('Chennai Express' team) are releasing a week apart, so I don't see any cause for stress. The fact is that nowadays films do a majority of their business on their first weekend (of release)," Imran told reporters here Tuesday at the cover launch of the stardust magazine.
"By the time you reach the second weekend, they already are trailing out, so it's not even a competition. The market has grown now, the exhibitors have multiplied ten-folds since the past, and there are a ridiculous number of theatres now," he added.
Directed by Rohit Shetty, "Chennai Express" is a comedy and features superstar Shah Rukh Khan and Deepika Padukone, while "Once Upon A Time In Mumbai Dobaara!", a period gangster drama, features Akshay Kumar and Sonakshi Sinha, besides Imran.
Meanwhile, with majority of the films doing well at the box office, Imran is not interested in tapping the economics.
"(I am) not at all (bothered by box office figures) because it ultimately makes difference to the producers and distributors (of the film)," said Imran, who has featured in popular films like "I Hate Luv Storys", "Mere Brother Ki Dulhan" and "Delhi Belly".
He says he sticks to what is an "actor's job".
"My job is to do my scenes from action to cut, then I have to turn up to promote my film, but beyond that it's not actually in my hands...the director is the one who is making the film, the producer is the one who is marketing the film. So these things are their expertise, and I don't enter into that space," he added.