The 26-year-old American, who recorded the first doping case in CBA's 17-year history, was banned for six months by the association on Monday, which means he will miss the rest of the season. His club Shanxi Zhongyu was fined 10,000 yuan (about 1,500 U.S. dollars).

Williams' agent Shen Zhiyu cited medical reasons for his marijuana use.

"Williams has been bothered by stomach problem for a long time so he brought some marijuana to China as a painkiller," said Shen.

"He suffered from a stomachache before the match and the medicine from the team doctor did not work," he said.

"So he had some marijuana and did not tell anyone," Shen added. Williams was drawn to take the test in the Dec. 9 match when Shanxi clinched a 103-99 away win at Jilin.

Williams apologized while he said he "let the team and the fans down" and "cherish" his playing days in Shanxi.

"I really cherish the opportunity playing for the team. I will always had them on my mind and keep watching the game," said Williams, who plans to return to the United States.

Then he said he would take the club as his first choice if he can come back. His contract with Shanxi runs until 2014.

"I definitely want to come back to Shanxi," he said.

Shanxi was also positive about the player's return.

"Williams had contributed a lot to Shanxi. Although he can no longer fulfil his task this season, the club will welcome him back next season as long as his return complies with CBA's regulations," said deputy general manager Zhang Beihai.

Marijuana was strictly controlled in China. In medical practice, doctors will use to relieve unbearable pain caused by cancer but anyone whose illegal possession or use will subject to detention and fine.