The 27-year-old joined the club back in January 2016 for £3.5million.

He scored seven goals in 39 appearance but never featured under boss Nuno Espirito Santo.

Mason had been on loan with Burton Albion, Colorado Rapids and Portsmouth in the past two seasons.

He was one of six departures on transfer deadline day.

Leo Bonatini (Nottingham Forest), Connor Ronan (FC DAC), Donovan Wilson (Exeter), Jack Ruddy (UD San Sebastian) and Phil Ofosu-Ayeh (Wurzburger Kickers) all moved out on loan, while Dominic Iorfa moved to Sheffield Wednesday for an undisclosed fee.