South Korean swimmer Park Tae-hwan will race alongside the defending Olympic champion in the 400m freestyle heat at the Rio de Janeiro Games on Saturday.
Park has been assigned the third lane in the sixth heat, with Sun Yang of China, the 2012 gold medalist, in the fourth lane.
Park is going for his third consecutive Olympic medal the 400m free. He was the champion in 2008 and won the silver behind Sun four years later.
Swimming in the fifth lane will be Connor Jaeger of the United States.
Sun has the second-fastest 400m time in the world this year with 3:43.55, followed by Jaeger with 3:43.79. Park is ranked sixth with 3:44.26.
Mack Horton of Australia, the world No. 1 with 3:41.65, is in the seventh heat.
The heats will start at 1:48 p.m. Saturday at Olympic Aquatics Stadium, and the final is scheduled for 10:30 p.m.