9:58 AM PT — Sources close to Gronk tell TMZ Sports his absence isn't personal, he's focusing on rehabbing his back after surgery.
We're told Gronk never did the movie as a serious stepping stone for his acting career, but rather as a favor for a friend involved in the production.
As one Gronk source put it, "Movie promotion is NOT a priority, his health and career are."
There is no lovefest behind the scenes of Rob Gronkowski's new movie — with one of his co-stars RIPPING the NFL star for botching his lines on set … and bailing on promoting the flick.
Joanna Krupa says she flew in from Poland for the premiere of "You Can't Have It" — in which Rob plays a cop investigating a violent situation at a bar — but Gronk's gone M.I.A. and she's pissed.
JK claims Gronk's done virtually no publicity and says, "To me, he's not a big team player."
We reached out to Gronk's camp for comment — so far, no word back.