The actors were originally lined up to shoot the final fight sequence in the film bare-chested, Mumbai Mirror reports.
"While Ajay who has got into a fine physical shape during Singham was all for it, Anil in spite of his best intentions, just couldn't," said a source.
Unlike contemporaries Shah Rukh Khan, Salman Khan and Aamir Khan, Kapoor has not revealed his physique for a number of years in his film work.
"Anil has always been shy about taking off his shirt," added the source.
The fight scene is set in London's St. Pancras station, which has been replicated in a Mumbai film studio.
Actor Zayed Khan has denied reports that the film is a remake of the Hollywood hit Speed.
Tezz, originally known by the working title Bullet Train, is expected to release in March.