Sun appealed that decision and WADA said in Wednesday’s statement it had been informed the Swiss Federal Tribunal had upheld a challenge against the Chair of the CAS Panel but had not made any comment on the substance of the case.
“WADA will take steps to present its case robustly again when the matter returns to the CAS Panel, which will be chaired by a different president,” the statement said.
The Tribunal was not immediately available for comment when contacted by Reuters.
Sun, the reigning world and Olympic champion in 200m freestyle, was banned after he and members of his entourage were found to have smashed vials containing blood samples taken at an out-of-competition test in September 2018.
Sun has questioned the credentials and identity of the testers, and has constantly proclaimed his innocence.
The 29-year-old, who won two gold medals at the 2012 London Games and another at Rio de Janeiro in 2016, is a controversial figure in the sport.
He served a three-month doping suspension in 2014 for taking the stimulant trimetazidine, which he said he took to treat a heart condition, while Australian swimmer Mack Horton openly called him a drug cheat at the 2016 Rio Olympics.
Horton refused to share the podium with Sun at the 2019 world championships in South Korea — a move that was applauded by other swimmers but condemned by FINA.