Manukainiu, 19, a redshirt freshman, and Vaenuku, 18, were killed, along with Andrew Uhatafe, 13, when the sport utility vehicle they were riding in with two other people ran off the road and rolled over several times Monday on U.S. Highway 550 in Sandoval County, New Mexico State Police said.
"We lost a terrific young man," Texas A&M head football Coach Kevin Sumlin said of Manukainiu. "Polo was loved by his teammates and coaches. Anyone who came in contact with him was struck by his sense of humor and smile. My heart aches for his mom and family members."
Manukainiu had posted a message on Twitter account Monday evening saying: "22 hour drive back to Texas on no sleep. Oh my."
Police said alcohol was not a factor in the crash, but the drive apparently was the only person in the vehicle wearing a seatbelt, ESPN reported.
Manukainiu and Uhatafe were ejected from the SUV and were dead at the scene. Vaenuku died in an ambulance en route to a hospital.
Offensive tackle Salesi Uhatafe, an incoming Utah freshman, survived the crash along with his father, Salesi Uhatafe Sr.
Manukainiu was the stepbrother of the younger Uhatafes. Manukainiu, Vaenuku and Uhatafe Jr. were teammates at Trinity High School in Euless, Texas.
"Heart hurts waking up to news about Polo," Aggies quarterback Johnny Manziel said in a tweet Tuesday. "I think I speak for everyone on our team when I say we love you brother you will be missed."