Klaasen confirmed on Wednesday he had taken up an offer from 41-year-old Paes, a 15-time Grand Slam champion in men’s and mixed doubles.
“Leander has won on the biggest stage many times, and this will be an opportunity for me to learn from one of the best doubles players of all time,” Klaasen said.
The South African, ranked 20th in the world in the two-man format, won three ATP titles with Butorac after they joined forces in September last year.
They also reached the final of the Australian Open and the quarterfinals of the US Open this season.
“If I wasn’t approached by Leander I would probably play with Eric next year,” Klaasen said.
“We did a lot of things well this season, but when someone with Leander’s success approaches you it’s hard to say no.”