Forbes was a central defender as a youngster at West Ham but has operated mainly at right-back for Rangers since his arrival two years ago.
Holloway confirmed "I want to have a look at him in that role. It's the right time to move him across.
"He came to us as a centre-back and ended up at right-back for various reasons and has done a good job there for me for two years now".
Forbes won the player of the season award at QPR in his first season at the club as Rangers climbed to an 8th place finish.