San Antonio, TX -- (Sports Network) - Welterweight Oscar Diaz underwent emergency surgery early Thursday morning for bleeding on the brain.

The fighter was rushed to University Hospital in San Antonio, a level one trauma center, after collapsing between rounds late in his nationally televised fight against Delvin Rodriguez on Wednesday.

"He was breathing and he has a blood pressure," Dr. Wayne Lee, one of the ringside physicians working the fight, told the San Antonio Express News. "But he was not responding to our commands."

Diaz (26-3) and Rodriguez (23-2-1, 14 KOs) were fighting for the vacant United States Boxing Association crown.