The fight between Amir Khan and Manny Pacquiao was guaranteed to take place at some point from the first time the pair sparred together in October 2008 at Freddie Roach’s Wild Card gym, a hard retreat in the seedy streets of West Hollywood.

Roach is a harsh man to hire as a new trainer and he threw Khan, who was fresh from a sixty-second knockout loss, to Pacquiao as a sacrifice on the Bolton boxer’s opening day in the gym. “People in the gym asked me if I was doing the right thing,” said Roach. “I was doing the only thing; I needed to know if Amir still wanted to be a boxer. I found out he did.”

Khan will fight Pacquiao on April 23 after an online poll rejected an Australian called Jeff Horn as Pacquiao’s next opponent, and voted overwhelmingly for a fight against Khan. The fight is set to take place on a Sunday, which would suggest that either Macau, the gambling island a short boat journey from Hong Kong, or the United Arab Emirates is the location.

Pacquiao, who is now 38 years-old, has fought twice in Macau, where it was thought he would be based after a lot of bold claims three or four years ago about the island replacing Las Vegas as the boxing capital of the world. However, Pacquiao’s last three fights have been in Las Vegas, including his disappointing loss to Floyd Mayweather in 2015. In theory, Pacquiao’s WBO welterweight title will be the secondary prize to the cash available, which would mean Khan fighting back in a weight division that makes sense; Khan fought in May last year when he gained nearly ten pounds and lost to Saul Canelo Alvarez at middleweight.

Khan had mentioned Old Trafford as a possible venue during the last three weeks of endless and often irrelevant rumours, but eight of his last nine fights have been in America. Pacquiao’s promoter Bob Arum is based in Las Vegas and he will look closely at the deals on offer from the various casino executives and the mysterious men in business cabals that back, sanction and fund the big fights in the Nevada city. There have been fights in Las Vegas on a Sunday - as happened between Joe Bugner and heavyweight contender Ron Lyle at Caesars in 1977 - but it is rare.

Manny Pacquiao in the ring against Jessie Vargas (Getty)

“When I sparred with Manny he was dangerous,” said Khan. “They were hard rounds and I knew then that one day I would fight him. I have been ready for a long time and I thought he was going to avoid me like Mayweather.” Khan was twice matched with Mayweather, once after a similar online poll placed him as the number one choice, and twice the negotiations fell short and collapsed.

Pacquiao has not stopped an opponent since 2009 and in several long fights, during the last few years, there have been poor performances and increasing concerns about his commitment to boxing because of his full-time work as a senator in the Philippine government. However, since the Mayweather flop, when Pacquiao suffered a shoulder injury early in the fight and seemed to float without anger to the last bell, his two wins have proved he is still a top operator.

Pacquiao and Khan pose after holding discussions about the possibility of a future fight, at Fitzroy Lodge Amateur Boxing Club on January 23, 2015 (Getty)

The fight will not be short of incident during the build-up with Roach, never the kindly uncle people want to imagine, sure to be critical of his former fighter; he firmly believes he rescued Khan’s career. Khan stopped working with Roach in 2012 and started to train under Virgil Hunter in the San Francisco area; part of the split was because of the increasing amount of time Roach devoted to Pacquiao, which included long training camps in remote regions of the Philippines. Khan had to travel to the camps, often working as a sparring partner when he had world title fights of his own.