(Reuters) - Twice major winner Jordan Spieth is still undecided about whether to participate in August's Rio de Janeiro Olympic Games or opt out because of the Zika virus like several of his fellow professionals. The American world number two is the highest-ranked golfer left in the field after number one Jason Day withdrew on Tuesday, citing concerns over Zika, a mosquito-borne virus that the World Health Organization says is spreading rapidly in the Americas. "Right now, I'm uncertain," Spieth told reporters ahead of the WGC-Bridgestone Invitational. More...