Andy Roddick has split with coach Dean Goldfine to work with his brother John.
Roddick is currently number three in the world
It will be the fourth coach in three years for the former US Open champion, who lost in the fourth round of the Australian Open last month.
After parting with long-time coach Tarik Benhabiles in 2003, Roddick worked with Brad Gilbert until December 2004, before teaming up with Goldfine.
John Roddick's first role will be to help his brother at this weekend's Davis Cup clash against Romania.
Six years older than Andy, John Roddick, 29, was an All-American tennis player at the University of Georgia and later coached there. He runs a tennis academy in San Antonio.
A former assistant coach with the US Davis Cup and Olympic teams, Goldfine guided Andy Roddick to a second successive Wimbledon final in 2005.
But the American has failed to win a second Grand Slam and crashed out in the first round of the US Open last year.