Bobby Cannavale plays the role of the recovering addict; Elizabeth Rodriguez plays his paramour.
A source who attended one of the play's readings said the funny role belongs to Cannavale, not Rock.
"It's high-octane, a real barrage of invective. The funny role is really Cannavale's, not Rock's," the source said in the Times. "He'll get laughs, I'm sure, but it's a role for a real actor, and it will be interesting to see him creating a character that is not himself."
Rock said he wanted the show to be an ensemble production, not a star vehicle.
"Chris does not want to be singled out as 'the star,' " the source said. "He wanted a good part, and he wanted to work with good actors. Scott delivered on both fronts."