The actor has developed his body for the project as the script contained a number of hand-to-hand combat scenes.
"Director Rohit Shetty therefore did not just want Ajay to develop a six pack which is easily achievable with injections and steroids; but to get a more realistic, brawny physique that would ooze raw manliness," a source said in a statement.
Devgn is reported to have worked with trainer Prashant Saawant for three months in order to make his body more lean and muscular.
The star also maintained a high-protein, low-carb diet during the training period.
Singham, a remake of a 2010 Tamil-language hit, is the first of four releases Devgn has planned in 2011.
The production, which pays homage to the age-old tradition of the Indian action film, is released on July 22.