He has previously played in Major League Baseball (MLB) for the Detroit Tigers and Boston Red Sox.

Villarreal signed with the Detroit Tigers and began his professional career in 2006, pitching for the VSL Marlins/Tigers and going 0–2 with a 3.48 ERA in 14 games (five starts).

On April 8, 2012, Villarreal was called up from Triple-A Toledo after Doug Fister went on the disabled list with an injured side.

On July 18, 2024, after nine years of inactivity, Villarreal signed with the Staten Island FerryHawks of the Atlantic League of Professional Baseball.

[9] Villarreal throws three pitches: a four-seam and two-seam fastball that tops out at about 100 mph, and a slider in the upper 80s.

[10] In March 2013, Villarreal's family home in Venezuela was attacked by three armed robbers who threatened to kidnap his relatives in the future.

The robbers had assaulted Villarreal's father and threatened to kill his mother and younger brother if they made any noise when officers arrived.