"MIKE & MOLLY" star MELISSA McCARTHY desperately wants to lose weight, but her bosses at CBS say “fat is funny” – and they want her to stay exactly the way she is!

“The way the network and producers look at it, the show’s funny because she’s fat – and it wouldn’t be if she wasn’t,” said a source. “She is contractually bound to stay tubby.”

Despite her ample size, Melissa, 42, insists that she leads a healthy lifestyle.

The star, who has two daughters – Vivian, 5, and 2-year-old Georgette – with her husband, actor Ben Fal­cone, plays tennis and does Pilates to keep fit. And she says her family eats healthy meals at home.

“Sometimes I wish I were just magi­cally a size 6 and I never had to give [my weight] a single thought,” the “Brides­maids” actress told a reporter recently. “I don’t really know why I’m not thinner than I am.”

Another close friend says Melissa’s excess bag­gage is taking a toll on her health.

“As she gets older, Melis­sa says she’s having a hard time breathing, and she’s starting to have pain in her knees,” the friend divulged.

As The ENQUIRER reported last month, Me­lissa’s runaway success has put her in high demand in Hollywood. She approached the network brass about letting her out of her contract to pursue film offers, but they put the kibosh on Melissa’s TinselTown dreams.

“Melissa would love to drop 40 pounds and focus on a career in films, but she’s stuck with at least another year on ‘Mike & Molly,’ ” added the source. “And her bosses there are re­fusing to let her lose weight. She feels stuck between a rock and a hard place.”