Fish will lead his Sacramento Capitals against the Orange County Breakers on July 13. Agassi's Boston team will travel to face John McEnroe and the New York Sportimes on July 19.
Williams, who won her fifth Wimbledon singles title on Saturday, will play her final match before heading to the London Olympics when the defending champion Washington Kastles host the Kansas City Explorers on July 22.
The eight-team, coed league starts Monday and runs through July 28. The WTT finals will be held Sept. 14-16, in Charleston, S.C.