O'Neill scored twice for Pompey in a 6 - 1 demolition of Leeds last season. He played in a couple of Premiership games last season and spent some time on loan at Walsall.
He played a major part in the two seasons leading up to Portsmouth's promotion to the top flight. He has made over 90 league appearances (staring and off the bench) and he's still just 21. He has scored 7 goals for Portsmouth.
O'Neil had been linked with a loan move to Wigan but City have snapped him up on a three month deal. Sheff Utd and Sunderland were also said to be chasing the midfielder.
O'Neil has played at England U19, 20 and 21 levels and has captained his country at U20 and U21.
An excellent signing and a second loan arrival in the space of a few days. Darren Williams from Sunderland being the other.
Good luck to Gary in his time at Ninian Park.