Muhammad Ali's Grandson Signs Modeling Deal ... With Huge Agency

Muhammad Ali always said he was pretty ... and now a huge modeling agency believes the good looks run in the family.

TMZ Sports has learned ... Ali's grandson, Biaggio Ali Walsh (son of Rasheda Ali Walsh), inked a deal with the Wilhelmina modeling agency ... one of the top modeling agencies in the world.

Wilhelmina has a pretty impressive roster ... with stars like Nick Jonas, Demi Lovato and Charlotte McKinney.

Now, we've confirmed the agency locked up 17-year-old Biaggio ... who also happens to be one of the top high school running backs in the country.

A Willy honcho tells us the agency believes Biaggio could have success in all facets of the industry -- "film, TV, commercial, print ... everything."

As one high-ranking Willy agent told us, "He has a great look. He's a well-rounded person. That's what we look for."