The American went so far as to inquire about it on Twitter, 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.
While Raonic didn’t respond to Williams as of yet, 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.