Matt Leinart: Baker Mayfield's Probably Gonna Win the Heisman

It's not a done deal ... but Matt Leinart says he'd really like Baker Mayfield to join him in the Heisman House.

"He's probably gonna win the Heisman, but we'll see in a couple of weeks," the USC legend told us at LAX.

As for Mayfield, the Oklahoma QB is wrapping up a pretty solid season -- he's thrown for more than 4,000 yards with 37 passing TDs and only 5 interceptions.

Leinart also weighed in on the college football playoffs -- and said he's a strong fan of EXPANDING from just 4 teams.