Serena Williams has re-ignited speculation that she could return to tennis (William WEST)World number one Aryna Sabalenka said it would be "cool" to see Serena Williams return to tennis after the American great refused to rule it out when asked, and instead replied: "I don't know. AdvertisementAdvertisement AdvertisementBut she re-entered the tennis anti-doping testing pool in December, setting off the rumour mill, only to deny that she was making a comeback. Asked about the prospect of Serena returning, Australian Open finalist Sabalenka said she had not spoken to anyone about it. "Serena denied (in December) she's coming back, but I think unless she gets injured there is no doubt she's going to play somewhere at some point. "Whether that's the mixed doubles at the US Open, whether that's doubles with her sister somewhere, whether it's singles, only she knows.