This will be his first time to defend his world title as he won it this January 2018 in a match versus Thai boxer Teerachai Sithmorseng when the welterweight championship was vacant of a holder.
"It serves as a big motivation for me to train and fight hard to win the crown", added Pacquiao, who has won eight world titles in a record eight weight divisions.
Manny Pacquiao enters this fight with a 59-7-2 record that includes 38 knockouts.
Asked about the reason Pacquiao chose to make a change - without notifying Roach - Koncz said, "There was some concerns Manny had in the last fight and some statements Freddie made to the media that Manny wasn't very pleased about". However, it goes without saying that Pacquiao is no longer the elite fighter he once was even just a few years ago.
Golden Boy Promotions' Oscar De La Hoya says that Pacquiao-Mathysse for the WBA welterweight world title is a done deal for July 15th in Malaysia. Pacquiao threw 573 punches in his last fight and landed 32 percent of them, so the hand speed and aggressiveness is still there and should be respected.
The 39-year-old Filipino senator and army colonel recently announced plans to launch his own cryptocurrency, and has been out of the ring since a controversial defeat to Australian Jeff Horn in Brisbane last summer.
"Hopefully this fight is a success and Manny is victorious, and possibly we can do a fight with (Vasiliy) Lomachenko in the fall".
Using the hashtag "Pacmanisback", the Philippine confirmed the fight on his Twitter account.
Pacquiao, 39, had said the fight against Matthysse would take place on June 24.
Promoted by Arum, Lomachenko, a former World Boxing Organization super featherweight champ, is set to challenge WBA lightweight titleholder Jorge Linares on May 12 at New York's famed Madison Square Garden.
"We had to schedule this fight so the senate wasn't in session and wouldn't interfere with Manny's training", Koncz said.