Serena Williams is a fan of Milos Raonic. Specifically, she loves the protective sleeve the hard-serving Canadian wears on his right arm.

The American went so far as to inquire about it on Twitter on Sunday while on a day off from the U.S. Open, asking Raonic if it would improve her serve (we suspect there was a touch of playfulness there as she leads the WTA in aces this year).  

What started as a legitimate health need has turned into a bit of a superstition for the fifth-seeded Raonic. Williams just thinks it looks stylish.

Here’s shot of Raonic wearing the sleeve.

Raonic didn’t respond to Williams as of yet, but he was asked Saturday if he believes the sleeve helps his play.

"I'm not going to argue when things are going OK," said Raonic, who breaks out the sleeve in different colours and patterns.

With files from The Associated Press