Brady Aiken announced Thursday that he had Tommy John surgery.

Aiken didn't sign a contract after the Houston Astros selected him with the No. 1 overall pick last year.

The 18-year-old was pitching for the IMG Academy, a private training institute in Florida, to prepare for this year's draft after the contract dispute with Houston.

"I'm obviously extremely disappointed," Aiken wrote for The Players' Tribune. "I wanted to let my pitching speak for itself, but now there are going to be new distractions. For that reason, I wanted to be the one to tell people what's happened and make this a fresh start."