Willis, 28, is looking to resurrect a career that's fallen on hard times since he won 22 games and finished second in the National League Cy Young Award balloting with the Florida Marlins in 2005.
The Marlins sent Willis to Detroit with Miguel Cabrera as part of an eight-player trade in December 2007. After signing a three-year, $29 million contract with the Tigers, Willis was diagnosed with an anxiety disorder and suffered from an inability to throw strikes.
The Tigers traded Willis to Arizona for pitcher Billy Buckner in June, but the Diamondbacks released him a month later. Willis hooked on briefly with the San Francisco Giants before hitting the open market as a free agent two weeks ago.
Jerry Crasnick is a senior writer for ESPN.com.