Vault champion Yang Hak-seon in doubt for Olympics

The 23-year-old, also a two-time vault world champion, became the first South Korean gymnast to win Olympic gold with his victory in London.

But an Achilles injury is set to rule him out of Rio, Korea Gymnastic Association official Han Chung-sik said.

"The rehab is expected to take three to four months," Han told Yonhap.

"Even if Yang recovers before the Olympics, he will not have had enough training to compete.

"He may demonstrate skills in the air, but it will be difficult for him to perform at the Olympics if he can't land well."

Yang won gold in Tokyo and Antwerp at the 2011 and 2013 world championships, with his London win in between.