Midfielder Bostwick, who has been playing as a centre-half, was forced off with a hamstring injury during the second half of Posh's 1-0 win at Blackpool prior to the international break and the problem has ruled him out of the last two games against Cardiff and Middlesbrough.
Manager Darren Ferguson will continue to check on Bostwick before Saturday's crucial clash in west Yorkshire.
Florent Cuvelier was included in both squads against Cardiff and Boro but the on-loan Stoke midfielder did not make it off the bench in either game and will hope to make his Peterborough debut at the John Smith's Stadium.
On-loan midfielder Alex Pritchard (ankle) is still not fit.
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