Ravel Morrison has returned to parent club West Ham from Cardiff City on compassionate leave.
Brighton boss Sami Hyypia is weighing up a move for former France captain Alou Diarra.
The 18-year-old has put pen to paper a one-year deal, with the option of a further 12 months.
Preston has been with the Blues academy for over five years.
He had a loan spell at Skrill North side Worcester City last season where he made two first-team appearances for the Dragons.