Walker follows Stenson exit from Houston Open 

First, Henrik Stenson pulled out of the Shell Houston Open with the flu. Now, Jimmy Walker has withdrawn from this week's tournament at the Golf Club at Houston, citing illness.
Walker won the Valero Texas Open on Sunday for his second US PGA Tour victory of the season. He then made a practice trip to Augusta National on Monday to prepare for next week's Masters. A day later, he officially withdrew from the Houston field, saying he had been laid low by a bout of flu.