The Scot had to be substituted just before half-time during the 2-0 Championship victory at Southampton on Monday night. Gallagher suffered with the injury earlier this season and boss Nigel Pearson is waiting to see what the damage is this time around.
He joins fellow midfielders Andy King (foot), Matt Oakley and Franck Moussa in the treatment room, while Michael Johnson is not fit enough for action and recent signing Danny Drinkwater is cup-tied.
Full-back Liam Moore has also played in the competition for another club this season during his loan spell at Bradford and Aston Villa have not granted permission for striker Nathan Delfouneso to play in the fourth-round tie.
Defenders Sol Bamba and John Pantsil are still away at the African Nations Cup with Ivory Coast and Ghana respectively and strikers Darius Vassell (knee), Jeffery Schlupp (knee) and Martyn Waghorn (hamstring) are injured.
Swindon will welcome defender Alan McCormack back into their matchday squad. McCormack has completed a two-match ban and could return to the heart of defence to partner Aden Flint, with Joe Devera making way.
Winger Luke Rooney will not be available to manager Paolo Di Canio, however, as the new signing from Gillingham is cup-tied, while the same applies for forward Billy Bodin.
Striker Mehdi Kerrouche will not feature for Di Canio, with the Algerian set to leave the County Ground this month having not played for the Robins since the 1-1 draw at Bristol Rovers on December 10.
Dutch wide man Etienne Esajas is struggling with a minor knock and will not be considered for selection.
Leicester V Swindon - view commentary, squad, and statictics of the game live.
Source: PA
