"He has the right to shop around to see if any other clubs will take him and maybe pay him more money," Allen told BBC Radio Gloucestershire. "Shane Duff's shown that he's a leader and he would be a good person to help bring our younger players on."
The Robins currently have only 13 professionals under contract for next season and Allen admits there are restrictions on the number of players he can bring in.
"There is a strict budget that we have to work to and we're not going to get into the position that we were in at the end of last season.
"We've got some very good youth players and they may have to be used more often."