Former lightweight world champion Juan “Baby Bull” Diaz of Houston has signed an 18-month promotional deal with Top Rank Inc., ESPN.com reported Thursday.

Diaz, 30, held three of the four major belts until he lost a split-decision to Nate Campbell in March 2008; it was Diaz’s first loss.

Diaz went 2-3 over his next five fights – losing twice to Juan Manuel Marquez and once to Paulie Malignaggi – before announcing his retirement after the second loss to Marquez in July 2010.

Diaz (37-4, 19 KOs) has fought twice since returning to the ring in April of this year. He is scheduled to take on Juan Santiago (14-10-1, 8 KOs) of Denver on Oct. 19 on the undercard of the Mike Alvarado-Ruslan Provodnikov junior welterweight interim title fight at 1stBank Center in Broomfield, Colo. (on HBO).