Tennis superstars Roger Federer and Serena Williams will not be taking part in the ongoing season of the International Premier Tennis League (IPTL). (Latest Tennis stories)”We are sad to announce that Roger Federer and Serena Williams won’t participate at the IPTL this year,” an IPTL statement read.IPTL founder and former India player Mahesh Bhuphati said he is hopeful of bringing the legendary players back on court in future seasons.”We have had challenges this year, and we were hoping to get past them. With the current economic climate in India and the uncertainty of spending money, I reached out to both Roger and Serena to explain the situation,” Bhupathi said.”They have been both been very supportive of the IPTL the first two seasons and we look forward to bring them in future years,” he added.FEDERER TROUBLED BY KNEE INJURYThe 17-time grand slam winner was expected to make a comeback on December 10 in Hyderabad with Indian Aces.Federer played his last competitive match was against Canada’s Milos Raonic in the semi-finals of the Wimbledon this year. After that he underwent knee surgery and that ruled him out of the Rio Olympics, US Open and the ATP World Tour Finals.Federer’s season was marred with injuries. He injured his knee while bathing his twin daughters after the Australian Open in February. A back problem forced him to pull out of French Open before a knee injury ruled him out of remaining 2016.SERENA RECUPERATING SHOULDER INJURYWorld No.2 Serena has also been out of action since US Open semi-finals defeat to Karolina Pliskova. Serena, who is tied with Steffi Graf on 22 Grand Slams, pulled out of the season-ending WTA Finals in Singapore in October as she wanted to focus on recuperating from a shoulder injury.advertisementSerena was expected to join the defending champions Singapore Slammers.