SERENA WILLIAMS’S Wimbledon appearance in women’s doubles with sister Venus is in doubt because of a knee injury.The 44-year-old made her return in singles after nearly four years away on Tuesday night to a rapturous Centre Court reception.Williams produced a strong display before fading in a 6-3 6-7 (6) 6-3 loss to 20-year-old Australian Maya Joint.There had been no indication during the match that the 23-time grand slam singles champion had hurt herself but she did not attend the customary post-match press conference, instead issuing a short quote.