The American, who could potentially face the 19-year-old in the Wimbledon quarter-finals, believes that the teenager has the potential to be one of the best in the world.
"She has an unbelievable game," The Mirror quotes Williams as saying. "She's so powerful. She's so positive. I think those are all qualities of what it takes to be a top player.
"Can she be a top 20 or top 10 player? I think she can go further than that."
Robson must win two matches in as many days to reach the fourth round of this year's competition after her second-round clash with Mariana Duque-Marino was rained off.