Floyd Mayweather Jr says he expects to be tested by Miguel Cotto when he takes on the WBA light-middleweight champion on May 5.
"Pretty Boy" had been desperate to get a fight in before he serves a 90-day jail sentence later on in the year and had challenged Manny Pacquiao to a much-anticipated super fight.
However, Pacquiao's camp said the Filipino fighter wouldn't be able to get ready in time and instead have penciled in a date in November for a showdown with Mayweather.
Mayweather has now turned to Cotto as he looks to make a step up in weight to become a six-weight world champion, the 34-year-old having not fought at light-middleweight since a controversial win over Oscar de la Hoya in 2007.
Cotto has held the WBA title since 2009 and apart from Pacquiao, represents the biggest threat to Mayweather's 42-fight unbeaten run.
Mayweather says he is ready for the challenge of making the step up in weight again and claims he is relishing the prospect.
"Miguel Cotto is a world-class fighter who can never be taken for granted and continues to prove he is one of the best in boxing," he said.
"It will be a challenge for me to compete with him at this weight, but this is the type of test I thrive on and gives me the motivation to train even harder.
"I have no doubt in my mind that my title belt collection will increase once again."