Robert Helenius has replaced Dillian Whyte to fight Anthony Joshua in London on Saturday.
The all-British heavyweight bout was cancelled last weekend following the adverse analytical findings detected in a doping test conducted by Whyte.
Meanwhile, the boxer has vowed to clear his name.
Helenius, 39, fought in his homeland on Saturday but has answered the call to take on the former two-time world heavyweight champion.
“This wasn’t in the script, “I respect Helenius and, may I say, I respect any male or female who steps into the ring.
“I am laser-focused on the win. I can make steps forward to bigger and better things but the road map has a check point — Saturday night. May the best man win,” Joshua said.
Helenius, who has 32 wins and four defeats from his 36 professional bouts, was knocked out in the first round by Deontay Wilder in October.
“I am a true Viking that is willing to face any challenge at a moment’s notice.
“This is not an opportunity I was going to let slip away. I plan to make the most of it,” said Helenius.
