Last Updated Feb 17, 2016 1:21 PM EST
Pacquiao denounced gay relationships in a TV interview in the Philippines, according to TMZ.com. "They know how to distinguish male from female. If we approve [of] male on male, female on female, then man is worse than animals."
The remarks quickly drew protests on social media. "I lost all respect for you," wrote Jason Collins, the first openly gay NBA player, wrote on Twitter. "Bigoted people like you (& yes you are one) should never hold an office in politics."
Pacquiao, 37, is running for a seat in the Philippines senate.
In another sign of the potential backlash for Nike, a petition on Change.org urged people to boycott the company until it drops Pacquiao as a client.
Pacquiao on Tuesday expressed regret for the slur, saying in a statement posted on his Twitter feed that "I'm sorry for hurting people by comparing homosexuals to animals. Please forgive me for those I've hurt."
On his Facebook page, Pacquiao also said he remains against same-sex marriage, while insisting that he is "not condemning" lesbian, gay, bisexual and transgender people. "God Bless you all and I'm praying for you," he wrote. Pacquiao, who has previously come out against same-sex marriage, also cited several Biblical passages against homosexuality.
TMZ reports that Nike is planning to end its commercial ties with Pacquiao, although no official decision has been made. Nike sells t-shirts, shorts, shoes and other gear emblazoned with the fighter's brand, "Team Pacquiao."
A spokesman for Nike did not immediately respond to a request for comment. The company is expected to issue a statement later today.