Christian McCaffrey Plays Santa For Olivia Culpo's Nephew, Adorable Video!

Not even a busted-up shoulder can take away the Christmas spirit from Christian McCaffrey ... the injured NFL star played Santa for Olivia Culpo's nephew -- and the vid is super sweet!

The Panthers running back -- who's currently out with a shoulder ailment -- jumped on FaceTime to pretend to be Kris Kringle for his GF's toddler nephew on Tuesday, and he CRUSHED the role.

Check out the footage Olivia posted of the cute moment ... McCaffrey made a white beard out of a blanket and had the little boy truly believing he was talking with Santa!

"Hey, Remi!," McCaffrey said on the phone. "Have you been a good boy this year?! I know you have! You've been a great boy!"

The two spoke for a while ... and McCaffrey ultimately promised him a truck and a bike for Christmas Day presents!

"My elves are going to work on it and we're going to fix it right up and put it under that great tree!"

#Adorable!

McCaffrey -- who's been dating Culpo for over a year now -- has played Santa for Olivia's nephew before ... and he appears to be killing it every step of the way as the swimsuit model's new man.