The 25-year-old full-back lasted just 11 minutes of the 3-1 win over Charlton on February 19 before suffering an injury in an aerial clash which forced him to sit out the 2-2 draw with Carlisle in midweek.
Liam Sercombe is expected to continue in Duffy's usual role following two impressive performances in his absence.
James Dunne is also a doubt after suffering a bruised leg against the Cumbrians despite only playing 21 minutes as a second-half substitute.
Daniel Nardiello, who has scored four goals in his last six appearances, three of which were as a substitute, is pushing for a recall after his 30-minute cameo in midweek and could replace John Flynn as the Grecians attempt to extend their unbeaten run to four games.
Winger Jake Thompson has joined Cheltenham on a month's loan.
Source: PA
Source: PA