Milos Raonic has withdrawn from Delray Beach with an adductor injury.
"I am still recovering from the injury I experienced at the Australian Open," he said in a statement.
In Melbourne, Raonic upset Stanislas Wawrinka in the fourth round in five sets and reached the semifinals, where he was injured during a five-set loss to Andy Murray.
The world No. 11 would have been the top seed at the ATP 250 event.
Tommy Haas has also withdrawn, having been sidelined with a shoulder injury for months. "I came to the conclusion I was not fit to play," he said.