WBO, WBA, IBF, IBO heavyweight world champion Anthony Joshua (22-0, 21 KOs) has warned WBC champion Deontay Wilder (40-0, 39 KOs) that he needs to "step up" or find himself on the sidelines on April 13.
The previously mentioned date has been set down for Joshua's next defense at Wembley Stadium in London.
Wilder is set to defend his title on December 1, when he faces unbeaten Tyson Fury in the main event of a Showtime Pay-Per-View from Staples Center in Los Angeles.
But on December 22 at The O2, Joshua will be ringside to potentially decide his next opponent - if a Wilder fight does not materialize.
That night, heavyweight rivals Dereck Chisora and Dillian Whyte will collide in a rematch of their 2016 slugfest, which saw Whyte win a razor-close twelve round decision.
Joshua, who back in September retained his belts with a knockout victory over Alexander Povetkin, is hoping that a Wilder bout can be nailed down, but he's already got his eyes on alternative opponents.
"I am not out again until next year, April 13. You know we're ready Wilder. Whatever, we are ready. Just be realistic on the negotiations because that's your issue not mine," Joshua told Sky Sports.
"It's a blessing to take myself out of training and go and watch these guys go and perform and see it from a different point of view. If I was a betting man? I want Chisora to win because he's my guy, north west London. I respect him. He's a Finchley ABC ambassador and he was a role model when I was coming through.
"And Dillian, I want him to win because I want to box him again. Come April 13, if Wilder doesn't step up, they're my two options. Good luck to Chisora, good luck to Whyte, they're both relevant wins for me."