Coach Mike Krzyzewski thinks it's time his Team USA squad got serious and his suddenly serious tone could have everything to do with the band of NBA superstar's next opponents.

After winning their first three tuneups for the upcoming Rio Olympics by an average of 45 points, the Americans next face a pair of 2015 FIBA World champions in Venezuela (July 29, in Chicago, 9 p.m. ET, NBA TV) and Nigeria (August 1, in Houston, 9 p.m.). You can watch a live stream of both games here.

Coach Sounds Alarm

Krzyzewski knew he had seen enough when DeMar DeRozan set sail on a contested 360 dunk against China and came up woefully short. Still, Team USA let the good times roll in their 107-57 annihilation.

Afterwards, Krzyzewski talked nonstop about how he let his team know it's time to tone things down and take matters far more seriously with much tougher competition lurking in the not too distant future.

That time could come as early as with Nigeria arriving in town. Led by star big man Ike Diogu and sharpshooter Josh Akognon, the team recently knocked off an Argentina team that features such present and former NBA vets as Manu Ginobili, Luis Scola, Carlos Delfino and Andres Nocioni.

On that night, Nigeria attempted 35 three-pointers, connecting on a more than respectable 15 of them.

Butler's Moment?

But between now and going face to face against the Nigerians, the Americans make a stop in Chicago to face Venezuela, allowing Bulls' star Jimmy Butler a chance to shine before his hometown fans.

Over the team's first three games, Butler has scored just eight points on nine shots, but the star swingman figures to have his number called much more often at the United Center.

"I know I'll be guarding, that's for sure," he said. "I don't think anybody's going to have the same role that they had with their individual team in the NBA. Like coach said, everybody has to sacrifice for the good of the team."

Complete Exhibition Schedule

USA 111, Argentina 74

USA 106, China 57

USA 107, China 57

USA vs. Venezuela - July 29 in Chicago (United Center) 9 p.m. ET

USA vs. Nigeria - Aug. 1 in Houston (Toyota Center) 8 p.m. ET