Donald will be making his eighth straight Open appearance, and the 16th overall of his career. His best result is a tie for fifth, both at Turnberry in 2009 and at Royal Lytham in 2012. The Englishman missed the cut in 2004, the last time the event was staged at Royal Troon.
No reason for van Zyl's withdrawal was given by the R&A when the field change was announced. Van Zyl is currently ranked No. 65 in the world and one of two golfers currently projected to represent South Africa in the Olympics.
Donald has slipped to No. 83 in the latest rankings, and he's hoping to spark a turnaround in his game beginning this week at the Aberdeen Asset Management Scottish Open.
"I've had some good success obviously at this tournament, and hopefully that will continue and hopefully that will set me up for The Open," Donald told reporters in Scotland. "My game is kind of built around 150 yards and in, and when I do that really well, then good things happen."
With Donald now in the field, Daniel Summerhays and Charles Howell III are first and second alternates, respectively, for The Open, which is scheduled for July 14-17 in Ayrshire, Scotland.