Ralph Lauren has announced it will end its sponsorship with Justin Thomas after golf's former world No.1 was heard muttering a homophobic slur after missing a putt last week in Hawaii.

Thomas, 27, has worn the company's clothing since he turned pro.

The US golfer has reached No.1 in the world on two occasions, won a major at age 24 and captured the high-profile FedEx Cup in 2017.

In the third round of the Sentry Tournament of Champions, he missed a five-foot par putt on the fourth hole and could be heard saying the slur under his breath as he tapped in.

Ralph Lauren said it was "disheartened" by his language.

"We believe in the dignity of all people, regardless of age, race, gender identity, ethnicity, political affiliation or sexual orientation," Ralph Lauren said in a statement.

"In reflecting on the responsibility we have to all of our stakeholders, we have decided to discontinue our sponsorship of Mr Thomas at this time."

Thomas was on an overseas vacation and could not immediately be contacted.

He is playing in Abu Dhabi next week on the European Tour.

He apologised after this third round, and again on Sunday when he finished one shot out of the play-off places.

"It's inexcusable," Thomas said.

"First off, I just apologise. I'm an adult. I'm a grown man, there's absolutely no reason for me to say anything like that. It's terrible.

"I'm extremely embarrassed. It's not who I am, it's not the kind of person that I am or anything that I do.

Unfortunately, I did it and I have to own up to it and I'm very apologetic."

Ralph Lauren acknowledged Thomas's apology but said "he is a paid ambassador of our brand and his actions conflict with the inclusive culture that we strive to uphold".

"Our hope is that Mr Thomas does the hard and necessary work in order to partner with us again - truly examining this incident, learning, growing and ultimately using his platform to promote inclusion."