David Haye will fight Vitali Klitschko this summer - if his brother Wladimir pulls out of their world heavyweight title unification showdown with injury.
Londoner Haye, the WBA heavyweight champion, finally agreed a deal to fight IBF/WBO king Wladimir over the weekend.
However, the Klitschkos' manager Bernd Boente has revealed that the contract signed does not specify which of the Ukrainian siblings he will meet.
Should Wladimir fail to recover from an abdominal injury before the end of June, Haye could instead fight his brother Vitali, the WBC champion.
Boente - who also confirmed they are exploring possible venues outside Germany for the fight on June 25 or July 2 - said: "It could also be Vitali.
"In the talks, David was not rejecting Vitali any more, he was very flexible. That was never negotiated.
"Knock on wood it's not the case, but should anything happen injury-wise (to Wladimir), as long as it is not three days before the fight or whatever, then Vitali could be the opponent. But first of all Vitali has to win his fight against Odlanier Solis on March 19 which will be a pretty tough fight."
While the contest was expected to be held in a football stadium in Germany, Boente revealed "two or three" options in other countries were also under consideration but insisted it would definitely not be in England or the United States.
"It is not 100% going to be in Germany," he said.
"The stadiums in Dortmund, Gelsenkirchen and Kaiserslautern are available and very interested in staging it.
"There are two or three other options that we are exploring in other countries. Honestly, that is only to maximise revenues. In the end it is not about home advantage or whatever. That is a key understanding between Adam (Booth, Haye's manager) and myself. Adam is with me in the driving seat, we will discuss these things together.
"We'll work out which stadium we use 100% as partners, be it in Germany or outside of Germany.
"I can't tell you where but they are all in Europe - but not England. Las Vegas and the United States was never an option because this fight has to be prime time in Europe, especially because the fight is pay-per-view.
"It will be around 10.15pm English time, 11.15pm German time. That is what we are looking for."
While Wladimir is expected to be in the opposite corner against Haye, there will inevitably be a degree of doubt after he twice pulled out of a voluntary title defence against Dereck Chisora with an abdominal injury.
He cancelled a fight against Haye's fellow Londoner in December after suffering the injury days before the bout and, despite rescheduling it for April 30, pulled out for a second time on Saturday because the problem is healing slowly.
Haye and the Klitschkos have been involved in on-off negotiations for more than two years - Haye himself withdrew from a 2009 fight against Wladimir with a back injury - and Boente revealed talks were far smoother this time around.
He also revealed the contract is a simple one-bout arrangement, with a general understanding that Haye would fight one brother first and then the other in the autumn, before his planned retirement in October.
"It is a one-fight deal. We didn't want to complicate it too much. Contrary to what was always said, in the end Adam and myself got along absolutely okay.
"The good thing this time was that the group of people negotiating and talking was very, very small.
"It was really just on their side Adam and his lawyer, and on ours Shelly Finkel (the Klitschkos' US advisor) and myself and it was very simple, very easy and we were really all acting as gentlemen. There were no problems.
"I think it is a very fair deal for both sides. Nobody can see himself as the winner or loser and if everything goes the right way from a revenue point we are all winners.
"It's a huge fight, not only for England, Germany and Ukraine but also for boxing fans around the world. It's one of the biggest, most massive fights with the biggest impact you can do at the moment, because nobody knows if the Floyd Mayweather-Manny Pacquiao fight will ever happen."
Boente revealed the definitive date for the bout will depend on where it is held.
"It really depends on the different stadiums, because not all of the three mentioned could do July 2. But those dates are agreed by the Hayemaker side and Sky."