Los Angeles Galaxy striker Landon Donovan has branded American swimmer Michael Phelps "a stud".

Phelps claimed his 20th Olympic medal on Thursday to stake a claim as the greatest ever American Olympic athlete, and Donovan was full of praise for his countryman.

"He's a stud. He's a champion, he's the greatest ever. With all that we hear about and read about him, the guy can still do it and it's impressive to see him as an athlete," Donovan told reporters.

The United States currently sit second in the Olympic medals table.