League sources told MassLive that Brady threw to "Gronk" on Monday. Gronkowski, who was in Los Angeles for a $50K charity basketball game at UCLA's Pauley Pavilion, confirmed the workout to TMZ Sports while attending the event.
"It was great working out," Gronkowski said. "Tom needs someone to throw to so, you know, he calls Mr. Reliable Robbie G the one and only."
Brady has brought in teammates and non-teammates for throwing sessions during the off-season, including suspended Patriots wide receiver Josh Gordon.
Gronkowski, 30, retired from the NFL in March after nine seasons in the league. The Pro Bowl pass-catcher told reporters at the beginning of June that he had no intentions of coming out of retirement.
In an interview with the NFL Network's Rich Eisen last week, Gronkowski softened his stance and cracked the door open on a possible return.
"There's definitely going to be times when you miss it and everything," Gronkowski said. "I would always say that it's still the off-season right now. I mean I can't really say how I'm going to feel about it when the games start rolling around and everything."
Gronkowski earned four first-team All-Pro nods and five Pro Bowls selections in his career. He also won three Super Bowl championships with the Patriots.
The All-Pro tight end caught 521 passes for 7,861 receiving yards and 79 touchdowns in 115 regular-season games with New England. The Patriots selected Gronkowski in the second round (No. 42 overall) of the 2010 NFL Draft out of Arizona.