Swiss tennis legend Roger Federer and Briton Andy Murray trained on a raft floating on the Limmat river here to promote the "Match for Africa 3" and to raise money for African children.
The game on Monday was organised by the Roger Federer Foundation, which manages several projects in Africa, reports Efe.
The match will take place later in the day between the world's No. 1 Murray and the world's No. 4 Federer at the Hallenstadion facility here.
During the raft training, Federer and Murray, who dressed in casual gear, had to hit the ball gently to prevent it from falling into the water.
The training attracted hundreds of viewers and was recorded by a drone.
Founded in 2003, the Roger Federer Foundation supports educational projects located in the region of southern Africa and Switzerland.
The programmes on the African continent focus on the improvement of the quality of early learning and basic education.