United have the option to recall the striker and sell him on to another club in the January transfer window.
But Sharp told the Sheffield Star: "I've signed until the end of the season and I want to see that out. Sheffield United can accept offers but I've got to accept terms.
"I'm happy here; I've got my career back on track and I've got a smile on my face. I'm enjoying it and when that happens I play my best football.
"I am a Sheffield United fan through and through and I'd love to be doing what I am doing here for Sheffield United. But I'm giving 110% to Doncaster at the moment and I am loving it."