Unable to fulfill his mandatory title defense, Timothy Bradley Jr. has vacated his welterweight world title.

Bradley was obligated to defend his 147-pound world title against Sadam Ali, but instead signed late last year to face Manny Pacquiao for a third time. Facing Pacquiao is much bigger in terms of profile and money compared with facing Ali, an unbeaten contender who is relatively unknown.

Bradley will face Pacquiao on April 9 in a 12-round HBO PPV headliner at the MGM Grand in Las Vegas, but without a world title at stake.

Bradley wrote a letter to WBO president Paco Valcarcel to formally relinquish the title on Feb. 4.

Timothy Bradley Jr. was unable to fulfill his mandatory title defense against Sadam Ali after committing to a third fight with Manny Pacquiao. Noah K. Murray/USA TODAY Sports

"As you know I will be fighting Manny Pacquiao on April 9, 2016 in Las Vegas, NV," Bradley wrote. "To accept this fight invariably means I cannot comply with my mandatory obligation and must forgo the mandatory against Sadam Ali, as ordered by the WBO. This is a difficult decision, but one I have to make to give fans the best fights as well as allow myself the toughest and biggest fights possible from both a competitive and financial perspective."

Bradley closed by writing, "I'd like to thank the WBO and its president Paco Valcarcel for their support throughout the years and for allowing me to represent the organization as a two-time world champion."

Bradley (33-1-1, 13 KOs), 32, of Palm Springs, California, won the WBO welterweight title twice and previously held its junior welterweight belt.

Valcarcel wrote back to Bradley on Tuesday.

"Do know that we wholly understand your decision and commend you for always giving fans the best fights possible and doing what is best for your career at this important juncture," Valcarcel wrote. "You have been an outstanding, honorable and loyal WBO junior welterweight and welterweight champion of the world and the doors of the WBO will always be open for you.

"Finally, I am pleased to inform you that we are preparing a special recognition for the Pacquiao vs. Bradley III winner -- two remarkable fighters and worthy ambassadors to the WBO. Wishing you all the best."

Ali (22-0, 13 KOs), a 27-year-old 2008 U.S. Olympian from Brooklyn, New York, will face former junior welterweight titlist Jessie Vargas (26-1, 9 KOs), 26, of Las Vegas, for a vacant title.

They will meet on March 5 on the undercard of the heavyweight fight between Luis Ortiz and Tony Thompson at the DC Armory in Washington, D.C. The card will be televised on HBO. Vargas previously challenged for the vacant belt, losing a decision to Bradley last June.