He has denied the accusations made by Chinese authorities who announced on Tuesday that the South Korea international was among 38 players banned.
Son, who had been playing for the Chinese Super League club Shandong Taishan FC, said he had given a false confession under duress to be freed from nearly 10 months of detention in harsh conditions.
"With the idea that we can no longer leave our fans who have been supporting the players and the team all year in confusion, the club has accepted a request by Son to terminate his contract that he made out of consideration for his teammates and fans," the club said in a statement.
Neither Son nor his agent could be immediately reached for comment.
He had said he hoped to continue his career with the Korea Football Association and signed for Suwon FC after he returned from China in March.
But his prospects became uncertain after South Korean media reported on Thursday that the CFA had referred his case to football's global governing body FIFA, which was expected to review it for possible disciplinary action.
