Yakubu was cup-tied as the Foxes lost to Manchester City on Tuesday night, while Vassell missed the third-round replay at Eastlands with a hamstring strain.
On-loan striker Yakubu is certain to come back into the reckoning but there is a slight doubt regarding Vassell`s inclusion.
Should Vassell be deemed fully fit, fellow forward Martyn Waghorn is expected to join Championship rivals Derby on loan.
Boss Sven-Goran Eriksson is also hopeful that Paul Gallagher will recover from the knee injury that forced him off after 30 minutes against Manchester City.
Franck Moussa or Matt Oakley are options for Eriksson should Gallagher not make it.