Mayweather and Pacquiao are trying to agree terms for what would be the most lucrative fight in boxing history.
If the two camps cannot come to an agreement, Espinoza has admitted that Khan and Cotto are the likely candidates to face the pound-for-pound king in Las Vegas on May 2.
Espinoza told NY Daily News: "He's definitely fighting on May 2. His first choice, by far, is Manny Pacquiao.
"If it becomes clear that that fight is not achievable, then he would move on to either Amir Khan or Miguel Cotto. He's made it clear to us that Pacquiao is still his number one priority, and that's where all our energy is focused."
Khan has frequently stated that he wants to face the unbeaten American, while Cotto lost to Mayweather by unanimous decision in 2012.