The Italian has been arguably the Owls' stand-out performer this season, contributing 12 goals and five assists in 25 appearances and his absence is certain to be felt.
That said, Carlos Carvalhal doesn't have a squad of 29 senior players for nothing, and the Portuguese has several options to consider before facing the R's - starting with these three:
Play Aiden McGeady
McGeady was signed for times like these and with Ross Wallace also impressing for the Owls, is unlikely to have too many opportunities as good as this one for which to stake a claim. The Irishman missed the Preston trip as he was not 100 per cent fit according to Carvalhal, who expects him to be fit for Tuesday. This would be a straight swap and perhaps the most likely outcome.
Bring back Jeremy Helan
Helan has made the squad just once since McGeady's arrival but while he may lack the technical quality of a Forestieri, McGeady or even Marco Matias, he can certainly match the Italian for energy. Helan was the solution when Forestieri was cup-tied against Arsenal earlier in the campaign and performed admirably.
Move Barry Bannan out wide
If Sam Hutchinson is fit - and not preferred to Vincent Sasso at centre-half - then this could certainly happen. It's a role in which Bannan has performed capably before, the only concern would be the additional disruption it could cause to the team - effectively being two changes rather than one.