Andy Zhang, a 14-year-old from China, is set to play in the U.S. Open.
Zhang made the field on Monday when Paul Casey withdrew because of a shoulder injury.
The United States Golf Association said Zhang will be the youngest competitor in the championship's history. Tadd Fujikawa previously held the distinction as a 15-year-old at Winged Foot in 2006, the USGA said.
Zhang will play alongside Hiroyuki Fujita and Mark Wilson for the first two rounds at San Francisco's Olympic Club.
Casey, 34, last played three weeks ago at the BMW PGA Championship, the flagship on the European Tour, where he missed the cut. It was his fifth missed cut worldwide this year.
The Englishman has finished just two events in 2012, and withdrew from the Players Championship due to injury. He was the second player to withdraw on Monday after an injured Brandt Snedeker also pulled out.