While shooting his new movie “Draft Day,” KEVIN COSTNER ended each day carefully viewing every foot of footage featuring him – not to review his acting chops, but to check for bald spots!

The star reportedly underwent hair transplant surgery years ago, but now he’s struggling with even more thinning areas, and cracked to his director and crew: “I have about three real hairs on my head – I call them Moe, Larry and Curly!”

Said an on-set source: “His hairdresser did her best to make sure his locks looked as natural as possible, but a few times they had to ‘thicken up’ by using various special products and coloring.

"Now Kevin makes sure his hairdresser always carries a big mirror so he can sneak a quick peek at his hair before each scene is shot!”