The Bible-quoting Pacquiao's description of gays as "worse than animals" drew criticism last month on social media at home and abroad, and cost him an endorsement deal with Nike, the world's largest sportswear maker.
The 37-year-old sitting congressman was ranked in the 11th to 14th position for 12 vacant seats in the upper house of Congress in a Feb. 15 to 20 survey, a drop from a January ranking of 8th to 10th place.
"There was a big drop in his numbers in the latest survey," Ronald Holmes, president of Pulse Asia, which did the survey of 1,800 people, told Reuters.
"It appears that his comments on the same-sex marriage issue had hurt his numbers, because it was widely reported in the media."
The Feb. survey showed 34.8 percent of respondents in favour of Pacquiao, down from 46.9 percent in January. Incumbent Senator Vicente Sotto, a television comedian, topped the polls, with 63.6 percent.
Pacquiao was not the only potential winning candidate whose rating fell, Holmes said. "His anti-gay comments could be the main reason," he said, but added that the survey had not questioned respondents about the reason for the change.
Many in the Philippines believe Pacquiao hurt some people's sensibilities with his remarks on same-sex marriage, which is not allowed in the country of 100 million people, 80 percent of them Roman Catholics.
There was no immediate response from Pacquiao, who is in training for what is being billed as his last professional boxing fight.
Senatorial poll rival, lawmaker Waldeon Bello, has asked the election commission to stop Pacquiao's WBO welterweight fight next month against American Timothy Bradley, as giving him an undue advertising advantage.
The poll body has yet to rule, but is weighing whether to set restrictions on broadcasts of the bout on April 9, exactly a month before the Philippine vote.
In the presidential race, Senator Grace Poe continued to dominate, despite a drop in her numbers to 26 percent from 30 percent in January. Vice President Jejomar Binay is catching up, in a statistical tie with 25 percent, up from 23 percent.
Southern city mayor Rodrigo Duterte and President Benigno Aquino's handpicked successor, former interior minister Manuel Roxas, have identical scores of 21 percent.
Less than three months from the election, about 4 percent of Filipinos are still undecided.
(Reporting by Manuel Mogato; Editing by Clarence Fernandez)
