The 48-year-old filmmaker took to Twitter to share the look on Rao's 32nd birthday.
"On his birthday a picture from @RajkummarRao's look test in our latest and most radical collaboration yet - OMERTA," he tweeted.
In another post he wrote, "To the honest, selfless and gifted actor whose visit to a reluctant me transformed my life. Many Happy Returns my dearest @RajkummarRao."
Rao and Mehta are known to share a good rapport as they have earlier worked in the three films together including "Aligarh," "CityLights" and "Shahid", which even got the actor a National Award.