Gennady “GGG” Golovkin and Canelo Alvarez, arguably boxing's two brightest stars, appear to be on a collision course to meet in the biggest fight of 2016. But the bout isn’t likely to happen until at least September, leaving the two middleweight title holders searching for an upcoming opponent.

Golovkin is set to fight next on April 23, while Alvarez will step in the ring again on May 7. No site has been determined for either bout, and even though they’ll be the sport’s biggest draws when Manny Pacquiao retires in April, they are having trouble securing opponents.

Billy Joe Saunders appeared to be the next man who would get a shot at Golovkin, perhaps the best pound-for-pound boxer in the world. The Kazakh superstar is on a mission to hold every middleweight belt, and he was looking to take Saunders’ WBO middleweight title that was won against Andy Lee in December. But a Golovkin-Saunder bout isn't expected to take place after negotiations stalled between the two sides in recent weeks.

The IBF mandates that Golovkin defend his middleweight title or be stripped of it. The organization lists Saunders as the top challenger for the belt, and Tuerano Johnson as the No.2 challenger. But Johnson suffered a shoulder injury and won’t be ready to fight in April, leaving inexperienced 25-year-old Dominic Wade as Golovkin’s most likely opponent. While Wade is undefeated and listed as the No.3 challenger, he would not pose a serious threat to Golovkin's perfect record.

For Alvarez, there aren’t many options for an opponent on Cinco de Mayo weekend. Golden Boy Promotions vice president Eric Gomez told earlier this month that he would meet with Alvarez in late January to discuss their future plans, but Gomez might not be able to find an opponent who would generate a significant amount of pay-per-view buys.

Floyd Mayweather Jr. recently told that he could defeat Alvarez for a second time if he got back in the ring, but he’s been retired since September and there are no concrete signs that he’d return for a shot at the middleweight champion. Alvarez could give Miguel Cotto a rematch for the middleweight title that he took from him in November, but the Puerto Rican boxer seems to have his eye on a few other opponents.

Cotto trainer Freddie Roach has suggested a few names to face the former champ and has floated veteran Mexican star Juan Manuel Marquez as a potential opponent. Marquez, 42, isn’t officially retired, but he hasn’t fought since 2014 because of injury concerns. Roach told Boxing News that the fight could take place between 147 and 150 pounds.

A fight between Saunders and Golovkin didn’t work out, but the Brit has expressed interest in facing either Cotto or Alvarez. Saunders is unbeaten in 23 fights, but his only significants wins, against Chris Eubank Jr. and Lee, were not convincing victories. 

Cotto avoided Golovkin when he held the middleweight title, and that fight won’t happen now as he considers fighting in a lower weight class. Golovkin promoter Tom Loeffler recently said that the champ will only defend his belt against Alvarez at 160 pounds. Alvarez’s last three bouts have come at a catchweight of 155 pounds.