Washington, Feb 3 : Olympic golden boy Michael Phelps' endorsement career is likely to take a downturn following photos showing him smoking marijuana out of a bong at a party, say market experts.

The pics published in Britain''s News of the World were taken in November at a University of South Carolina house party.

Robert Tuchman, president of Premiere Corporate Events, a sports entertainment firm said that the scandal is likely to hit eight Olympic gold medallist's advertising career.

"It''s certainly not good and it's a disaster in terms of the near future," Fox News quoted Tuchman as saying.

"He''s very unlikely to have new sponsors come on board and endorse him. And there''s the potential for other sponsors to pull the plug on him, using this is an opportunity. He''s going to take a big hit on this," he added.

However, the 23-year-old swimmer has already apologised for his inappropriate conduct, citing his age as an excuse for his poor judgment.

"When these brands make an investment in you, they make a serious investment in you and it doesn''t matter what age you are," Tuchman said.

"He kind of used that as an excuse in his apology, but these companies are paying him a lot of money and they have a right to hope that he continues to be seen in a positive light," he added.

Two of Phelps'' endorsement deals - with AT&T and Rosetta Stone - ended on December 31, 2008.

AT&T officials refused to comment on any plans to re-sign Phelps; a Rosetta Stone spokeswoman said Phelps is not being considered for future promotions, but that decision was made before the photo surfaced.

"We do not condone his activities and are disappointed in his recent judgment," a statement issued by Stone read.

However, two of Phelps'' leading sponsors indicated they are sticking by him. Swiss watchmaker Omega said Phelps'' actions were a private matter and a "nonissue," while swimwear manufacturer Speedo called him a "valued member of the Speedo team." (ANI)