Joshua set to face Finland's Helenius as late Whyte replacement
The scheduled all-British heavyweight bout was cancelled last weekend when "adverse analytical findings" were detected in a doping test conducted by Whyte, who 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," said Joshua. "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."
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," said Helenius.
"This is not an opportunity I was going to let slip away. I plan to make the most of it!"
