The Welshman is suffering from a knee injury and was substituted in the 3-0 defeat at QPR.
Defender Shane Lowry is nearing a return to fitness after missing the Loftus Road defeat with a knee problem.
But Lee Williamson will definitely miss out through suspension as he serves the second match of his four-game ban.
Three players left Bramall Lane on Thursday, with Richard Wright and Stephen Jordan having their contracts terminated by mutual consent and loanee Jean Calve returning to parent club AS Nancy.
United's survival hopes are hanging by a thread, with the club seven points adrift of safety with just seven games to go.