The 34-year-old, who boasts over 400 senior appearances and 170 goals in his career to date, has been without a club since leaving
Turkish side Kayserispor last year.
"We're pleased to have secured the signing of Yakubu, who brings vast experience and a terrific goal record," Slade told the club's official website.
"His professional career speaks for itself, having scored consistently at the highest level of English football, and will act as a superb role model for the younger players.
"He is astute on the ball, has clear quality and presence, and we'll continue to work on his match fitness as we prepare for the final 16 games of this season."
Yakubu, capped 57 times at international level with Nigeria, has also previously represented Portsmouth, Leicester City, Blackburn Rovers and Reading.