Jennifer Aniston has been spending $20,000-a-month on beauty treatments since she started dating John Mayer, a new report claims.

According to America’s National Enquirer magazine, the former ‘Friends’ actress is so keen to look good for her man — she’ll do whatever’s necessary to avoid going under the knife.

A source told the publication, “Jen is doing whatever it takes to hold back time – short of plastic surgery.”

The 39-year-old’s regimen, says the Enquirer, includes private instruction with top yoga guru Mandy Ingber, and personal training sessions, both done three times a week — at a cost of about $3,000.

Jen also pays a private chef $3,500 a month for organic, high-protein, low-fat meals.

“Jen is insecure about her legs, so she goes for anti-cellulite spa sculpting treatments twice a month,” revealed the friend.

“They cost $1,000 a session, but Jen swears that the sculpting keeps her skin supple and smooth.

“She calls the treatments ‘necessary tune-ups.”