During his time at USC, he received high praise from teammate Carson Palmer, a future NFL star QB who said of Mattos: "Having a guy like Grant Mattos come in has been great, he's really gonna set the tone for the receivers. He's out there working harder than anyone on this team and he'll catch any ball, his hands are unbelievable. He's big and physical too so we can put him at tight end or receiver and he's strong enough to do both. It's gonna be exciting to see what he does this year. His story of how he got here is amazing, I'm not surprised at all that Coach Chow went out and found some guy from some place and brought him in with a chance to start" "He has awesome hands and he doesn't drop anything. He's a lot like (ex-USC receiver) Matt Nickels. Only he has more potential. He's bigger and stronger and capable of more."