Mark Mulder, who retired in 2009 after a pair of surgeries on his left shoulder, is attempting a comeback at 36.
Mulder has been working at ESPN as an analyst since 2011.
The idea for a comeback was born when Mulder watched Los Angeles Dodgers reliever Paco Rodriguez on TV and found something in Rodriguez's delivery that he could emulate.
The left-hander recently threw off the mound for three unspecified teams near his home in Scottsdale.
"I can't even begin to tell you how excited I am," Mulder said. "To be honest with you, I never anticipated this five or six weeks ago. It was just a flat-out fluke that came from me trying to imitate Paco Rodriguez in my living room."