US swimming star Michael Phelps has posted a video clip vowing to make his Chinese fans proud of him again after a photograph was published appearing to show him smoking marijuana.
"To my Chinese friends, as many of you know, I recently engaged in a behaviour which was regrettable and not what people have come to expect from me," Phelps said as he began a one-minute message posted on websites in China.
"The past few days have been tough for me, but I've received support and encouragement online from so many Chinese friends. I will learn from these mistakes, train hard, and make you proud again."
Phelps, 23, achieved sporting immortality in China last year when he won an unprecedented eight gold medals at the Beijing Olympics, adding to a haul of six in Athens.
But he has been under intense scrutiny since British tabloid News of the World last week published a photograph of him with his lips pressed to a glass pipe of the kind used to smoke marijuana.
The newspaper said the photo was taken at a university party in South Carolina in November.
Phelps had already apologised for using "bad judgement" and letting down his legion of fans.
In his video message to Chinese fans, he said "the warmth and the forgiveness" from them had lifted him.
"Thanks again for your support and your encouragement," he said.
Phelps recently signed a sponsorship deal with Mazda to endorse the car company in China.
Although no figures were announced, it was reported to be worth more than one million dollars, making it the biggest sponsorship deal for a foreigner in China.
Mazda on Thursday issued a statement saying it would continue to endorse Phelps, while highlighting the importance of his video apology posted the previous day.
"His expression of remorse and his determination to make amends, and especially his video apology and expression of thanks to the Chinese people, give us confidence that Phelps can make a healthy return to the pool and have even more brilliant achievements," the company said.
"We will continue our cooperation with Phelps."
US food company Kellogg's has already said it will not renew its endorsement deal with him.
But others, such as swimwear manufacturer Speedo and watchmaker Omega, have stuck by him.