The 26-year-old can leave Ibrox on a free with Bolton and Charlton having monitored his situation this year, Press Association Sport understands.
He has already turned down a move to Southend in the hope he could still play a part at Rangers and feature in Europe, before they went out of the Europa League to Luxembourg part-timers Progres Niederkorn.
Charlton made an offer for Forrester but nothing was finalised, while Burton have been linked but have not made an approach.
Forrester was told by Rangers boss Pedro Caixinha two months ago he had no future at the Ladbrokes Premiership club, despite having two years left on his contract.
The former Doncaster midfielder also disputed reports in June he had been suspended by Rangers for a poor attitude by writing on Twitter: “Rumours and reports that I have been suspended are totally false and inaccurate.”
Forrester, who is keen to return south, signed a three-year deal at Rangers 15 months ago and helped them return to the Premiership last year, netting five times in 16 appearances.
He played 28 times in the league for the Light Blues last season and has scored seven goals in 13 league starts, making 44 appearances in all competitions.