Agyemang, who has scored three goals this season, is set to go straight into the Robins' squad for Tuesday night's visit of Cardiff, subject to Football League approval.
He has made 61 appearances for Rangers, scoring 14 goals.
The latest gossip and rumours from the newspapers and online:The Sun says Chelsea striker DIEGO COSTA will call a truce
Pep Guardiola conceded Manchester City's Premier League title bid could be over after the heaviest domestic league defeat of his
It feels right again said Gary Neville, after United secured a 2-1 victory over Middlesbrough with an 86th minute winner
Wayne Rooney has the chance to officially break Sir Bobby Charlton's Manchester United all-time scoring record on Sunday - but
Manchester United host arch-rivals Liverpool at Old Trafford on Sunday.
It may only be a couple of weeks old but 2017 hasnt been a good year so far for Liverpool.