Anthony Joshua labelled Deontay Wilder a "fool" and called out the American and Tyson Fury following the duo's contentious Los Angeles draw.
Wilder retained his WBC heavyweight title after the judges returned a split decision that earned much ire from pundits and fans, with most considering Fury the victor despite having to twice climb off the canvas.
It now remains to be seen what direction Wilder goes in, with a rematch against Fury and the winner facing Joshua later in 2019 one possibility.
Earlier this week, Wilder's co-manager Shelly Finkel said the 33-year-old was "very interested" in fighting Joshua.
The unbeaten Briton, whose camp failed to reach agreement with Wilder's for a 2018 showdown, has now responded to those comments and said he is ready to face either of his heavyweight rivals.
"What took this fool so long? Like we ain't been interested?!!" Joshua, the IBF, WBA and WBO champion posted on Twitter.
"Anyway well done Fury! They wanted to get you because they assumed you was finished!!
"I'll give you a fair one when your (sic) ready! Either one of you!"
Joshua last fought in September, when he successfully defended his belts by stopping Alexander Povetkin in seven rounds at Wembley.
Fury claimed Joshua would have been "nailed" by Wilder, and said his domestic rival has "my belts" - a reference to the titles he held after defeating Wladimir Klitschko in 2015 before relinquishing them due to inactivity.