Fedor Emelianenko was expecting to see Frank Mir in the Windy City. What he wasn't expecting was the FBI to show up and knock on the door of his hotel suite here. No one knows why, and no one wants to discuss it.

But officers from the Federal Bureau of Investigation are here, and they are talking to the man widely regarded as mixed martial arts' heavyweight 'GOAT'.

There is no suggestion that Fedor is in trouble with the FBI. But no one has a word to say about it. Not the officials overseeing the Bellator 198 event. They don't know why. Not Fedor, nor his team. Not a word from the FBI, either.

Stum. No comment all round. But the theories, for what they are worth, are plentiful and plausible.

Here's what happened: on Tuesday, Fedor arrived into Chicago with his team - a group of around twelve in the entourage, including his translator - after a training camp spent largely in Amsterdam, in preparation for his headline fight in Bellator's heavyweight World Grand Prix tournament against Mr Mir, the former two-time UFC champion. Both men have been decorated champions, and are close to the end of their careers.

Three days ago, while the mixed martial arts legend was taking a walk outside in the vicinity with some members of his entourage, officials from the FBI turned up at the hotel, requested to see him, and knocked on his room. They waited for him. They spoke with him. They have, by some accounts, been in and out in the last few days.