Khan can beat 'slowing' Floyd this year - Roach
Khan had been due to face Peterson on May 19 for the WBA and IBF light-welterweight titles, but that contest was scrapped after it was revealed Peterson failed a drugs test.
The Bolton fighter is now expected to be back in action in late June or early July against WBC king Danny Garcia, who beat Mexican legend Erik Morales in his most recent outing.
The WBA and IBF crowns are also expected to be on the line, and Khan will hope to leave the 140lbs division with three titles.
If he does that, he will represent an enticing welterweight opponent for Mayweather, who said before his triumph over Miguel Cotto last weekend that he was keeping a keen eye on Khan's progress.
And Roach feels that a battle against Mayweather, the unbeaten American often called the planet's pound-for-pound king, is very winnable for Khan.
"If it's Garcia, Amir will be too fast and hard-punching for him," Roach told the Daily Mail. "Whoever it is, we'll do this one more fight and then go up to welterweight to look for Floyd Mayweather. I see Floyd's legs beginning to go [at 35] and him slowing up a little. If we get him as early as December, Amir can beat him."