Ryan Dickson, who had been struggling with a hamstring problem, trained last week and managed to start Friday’s 1-1 League One draw at Millwall.
But the midfielder lasted just 18 minutes before suffering another hamstring injury and manager Andy Scott admits he is unlikely to be fit to face the Grecians.
Kevin O’Connor was also substituted against the Lions and required stitches in his ankle, while Charlie MacDonald sustained a head injury.
Scott may struggle to name seven substitutes but admitted there were players who were putting themselves through the pain barrier.
The Bees boss, who will complete a two-match touchline ban for improper conduct, will again be without Mark Phillips (knee) and Nikki Bull (shoulder).