World Series of Fighting is making some changes.

Thiago Silva will take on Matt Hamill in a rematch that will act as the WSOF 19 co-headliner March 28 in Phoenix, WSOF president Ray Sefo told MMAFighting.com's Ariel Helwani on Tuesday. The bout will be a semifinal in the WSOF light heavyweight title tournament.

Vinny Magalhaes was initially supposed to face Hamill in the main event of World Series of Fighting 20 on April 10 at Foxwoods Resort Casino in Connecticut, but according to WSOF there are issues with his contract. Magalhaes is currently the Titan FC light heavyweight champion and the promotion is trying to keep him on board. Request for comment from a Titan representative was not immediately returned Tuesday evening.

Silva (16-3, 2 NC) was going to fight Ronny Markes at WSOF 19 on March 28. Now, Markes will be moved to a different card against an opponent to be determined. Markes will still be a part of the 205-pound title tournament.

The new main event for WSOF 20 has not been announced yet.

Silva beat Hamill in his last fight by unanimous decision at UFC Fight Night: Maia vs. Shields in October 2013. Since then, the Brazilian has dealt with injuries and domestic issues with his ex-wife Thayse Kamiji that eventually got him released by the UFC. Silva, 32, is unbeaten in his last three fights.

Hamill (11-5) has also not fought since October 2013. He retired thereafter, but announced his comeback with WSOF last year. The inspirational fighter, who was born deaf, has lost three of his last four bouts. But the 38-year-old Hamill has notable wins over Tito Ortiz, Mark Munoz and Tim Boetsch -- not to mention the infamous disqualification victory over Jon Jones.

As for Magalhaes (12-7, 1 NC), he won the Titan light heavyweight title from Jason Brilz last September. Magalhaes said on Twitter he is currently a WSOF fighter, but would not give further comment.

WSOF 19's main event will remain a lightweight title fight between champion Justin Gaethje and Luis Palomino.

WSOF 20's co-headliner is still set to be UFC veteran Melvin Guillard taking on Ozzy Dugulubgov. Nick Newell will meet Joe Condon on the card as well.