Days after Us Weekly reported that Hudson, 31, had a small breast augmentation, the actress showed off her new chest at Coachella over the weekend.
But the 26-year-old Pratt, whose wife Heidi now has a "E or F" bra size following her infamous 10 operations-in-a-day, isn't impressed.
"How is it possible to get breast implants and still not have breasts," he Twittered Monday. "Kate H - get ur money back..."
Referring to Dr. Frank Ryan (who performed Montag's surgeries), Pratt then added, "I gotta guy who will hook you up!"
In another message, Pratt took aim at Robert Rey -- a.k.a. Dr. 90210 -- who tells UsMagazine.com that Montag, 23, is sending a bad message to girls for altering her appearance so drastically. Pratt says Dr. 90210 is a hypocrite because his daughter is "into plastic."