I googled Gavin Gunning and found this on Wikipedia:
"On 12 April 2016, Dundee United announced that Gunning had left the club by mutual consent, describing the decision as "a private matter". This came three days after a match against Inverness Caledonian Thistle during which Gunning, in what was described by the media as "a bizarre incident", had picked up the ball during play and walked off the pitch. He subsequently returned to the field to receive treatment for an injury before being substituted. It was reported that he had "sarcastically applauded" fans who verbally abused him over his conduct. Despite the club statement, manager Mixu Paatelainen subsequently clarified that while Gunning would not be considered for selection, he remained a Dundee United player and could return to training if he wished "or take an early summer holiday".
Perhaps he's a reformed character now and Richie will know how to get the best out of his fellow countryman?