Floyd Mayweather Jr is set to finish his career with a fight against Andre Berto on September 12 at the MGM Grand in Las Vegas.

Mayweather announced the fight on Tuesday via social media, with the 38-year-old undefeated boxer set to make his first appearance in the ring since his unanimous points decision victory over Manny Pacquiao in May.

Berto - a two-time welterweight champion - holds a 30-3 professional win-loss record, including 23 knockout victories, with the Haitian-American having won his past two fights, including the knockout of Josesito Lopez in March.

But the 31-year-old's form has been inconsistent over the past four years, with three wins and three defeats since the start of 2011.

In June, Mayweather revealed his final fight would be against either Berto or Karim Mayfield.

Mayweather had been linked with a potential rematch with Pacquiao, while British boxer Amir Khan had been very vocal in his desire to fight the man known as 'Money'.

September's bout will be the 49th professional fight of Mayweather's career - with the Michigan-born pugilist having won all previous 48 bouts, including 26 knockouts.

Speaking after the Pacquiao fight, Mayweather said: "My last fight is in September, then it's time for me to hang it up.

"I'm almost 40 years old now, I've been in the sport 19 years, I've been a world champion 18 years and I'm truly, truly thankful and I'm blessed."