Khan will face Alexander in Las Vegas in the hope of earning a future bout with either Mayweather or Pacquiao, the former having regularly evaded a meeting with the Briton.
Mayweather opted to fight Argentine Marcos Maidana twice in 2014 over facing Khan and is expected to retire next year following the remaining two fights on his Showtime television contract.
But De La Hoya says the 27-year-old boxer will not have to wait long to secure the long-awaited bout.
"I expect him to get the Mayweather fight," the Mexican said. "He has been wanting the major names in boxing for quite a while. He deserves it.
"This is a tough fight that neither can look past but obviously the big prize is the Pacquiaos of this world and the Mayweathers of this world. There is a lot on the line, this is high stakes."
After outclassing Luis Collazo last May, Khan has dodged a fight with fellow Briton Kell Brook in order to secure a bout with Alexander but, despite being linked with a future meeting with Mayweather, he is refusing to look to the future.
"I'm not focusing on anything other than Alexander," he said. "I've made the mistake of looking too far ahead before. If I beat Devon, I know the next fight will big, even bigger and better, but I have to win first. There is a lot to gain for both of us: we can both get a superfight.
"This would have been an amazing fight for me 12 months ago when he had a world title but it is still a big fight for me. Devon is one of the A-class fighters in the welterweight division.
"I don't like to look backwards because [not taking the fight meant] I had 12 months out of the ring, which was tough for me.
"But I had a good break and gave me a chance to work on things and build up my strength when I moved up to the welterweight division, so I am strong at the weight rather than just rushing up. I will be much better at the weight against Devon than I would have been 12 months ago."