:focal(1126x863:1128x861)/origin-imgresizer.eurosport.com/2019/05/14/2587470-53648110-2560-1440.jpg)
The 37-year-old American world number 11 had been due to face sister Venus in an eagerly-awaited second-round clash in Rome. Venus received a walkover into the third round.
“I must withdraw from the Italian Open due to pain in my left knee,” the 37-year-old said.
Serena Williams (USA) in action against Rebecca Peterson (SWE) during Internazionali BNL D'Italia Italian Open at the Foro Italico, Rome, Italy on 13 May 2019.
Image credit: Getty Images
“I will miss the fans and competition at one of my favourite tournaments.
“ I’ll be concentrating on rehab and look forward to seeing you all at the French Open and next year in Rome.
Serena Williams (USA) in action against Rebecca Peterson (SWE) during Internazionali BNL D'Italia Italian Open at the Foro Italico, Rome, Italy on 13 May 2019
Image credit: Getty Images
Serena, a 23-times Grand Slam singles champion, has struggled throughout the year and completed only two matches since the Australian Open where she reached the quarter-finals.