Dexter Pittman, a senior at Texas and former Longhorns center, left the NBA draft combine Friday.
Darius Johnson, Pittman's 15-year-old brother, was shot during a confrontation in Katy, Texas, and later died at a hospital.
Harris County Sheriff's Department spokeswoman Janie Wagner said a deputy was sent to the home just before 10 p.m. Thursday. The deputy found the victim "in the garage in his residence sitting in a chair with a gunshot wound to his head."
Wagner said the case is being investigated as a homicide. She had no other details and said the department wasn't identifying the victim because he was a juvenile.
An investigator with the Harris County medical examiner said an autopsy was planned Friday.
The NBA released a statement that Pittman would not participate in Friday's combine because of a family emergency.
Johnson was one of Pittman's three siblings. Pittman was informed his brother was shot at midnight ET Thursday. Pittman arrived in Houston midmorning Friday, where he was informed by his mother that his brother had died.
"I just feel terrible for him. Dexter has gone through so much to get to this point, he was in the best shape of his life, he worked so hard, and then this tragedy happens," said Mark Bartelstein, Pittman's agent.
Texas assistant Rodney Terry, who has been close to Pittman, said Dexter had been trying to get his brother Darius "on track. He had really worked hard to keep him out of trouble. So did his mom. He did everything he could. It's just so sad."
Terry said Darius was rushed to the hospital after the shooting but attempts to save his life weren't successful.
"Obviously the thoughts and prayers of all of us associated with the University of Texas basketball program are with Dexter Pittman and his family," Texas coach Rick Barnes said in a statement. "We know that this is a very difficult time for them."
Andy Katz is a senior college basketball writer for ESPN.com. The Associated Press contributed to this report.