Bennett had to go off after just six minutes of the 2-1 defeat at Bristol Rovers with a knee injury.
"Rhys has damaged a knee and it doesn't look good," said Hill.
"We will know more after a scan, but it could be a season-ending injury."
Michael Rose came on for Bennett and scored Dale's equaliser after Ellis Harrison's fine opener.
But teenage winger Harrison bagged the winner with his second six minutes from time.
"We created some great opportunities, which I am pleased about, but failed to take them," added Hill.
"George Donnelly could easily be going home with the match ball for a hat-trick. Instead we are reflecting on a game we should never have lost.
"If you can't win a game you have to draw it. We made some poor decisions after getting the equaliser and I was looking for some leadership out there."