The on-loan striker missed the Hornets' 2-1 defeat to Hull after picking up a hamstring injury in training ahead of the game, and remains a doubt.
Fellow Udinese striker Matej Vydra was selected in Forestieri's place against the Tigers and is expected to be handed another start alongside Troy Deeney, who will equal a club record if he finds the net for the seventh successive game.
Midfielder John Eustace has returned to training following a back injury, but the trip to Turf Moor will come too soon for a return. Fellow midfielder Prince Buaben completed 45 minutes for the reserves in midweek on his return from a thigh injury, but is not expected to be involved.
Defenders Lloyd Doyley and Nyron Nosworthy remain sidelined with hamstring problems.