 However, since there were no spaces remaining in the club's A-League squad, Mullen was only eligible to participate in Western Sydney Wanderers' 2014 AFC Champions League campaign during the 2013–14 season.On 18 March 2014, following a long-term injury to Golgol Mebrahtu, Mullen was added to Western Sydney Wanderers' A-League squad.Mullen parted ways with the Wanderers on 30 January 2015.