The forward missed the home win over Millwall nine days ago with a knee injury sustained during the FA Cup replay defeat to Manchester City at Eastlands.
Should Gallagher be fit it could pave the way for Martyn Waghorn to leave the club ahead of the 11pm transfer deadline, especially following the loan signing of Daniel Uchechi from FC Dender.
Uchechi could be involved at Bramall Lane, while Chelsea left-back Patrick Van Aanholt is in line to make his debut.
Franck Moussa, Matt Oakley and Steve Howard are options for boss Sven-Goran Eriksson should he wish to make further changes.
Source: PA
Source: PA