McGrain continued to be a mainstay of the Celtic side during the early to mid 1980s; captaining them to a further three league championships, two Scottish Cups and one Scottish League Cup, despite also suffering a broken leg in 1981. He made his 600th competitive appearance for Celtic in a 2–0 win over St Mirren in October 1985. Manager Davie Hay described him as a "superb player and professional" and said he was "the best tackler on the field" in the match against St Mirren. In the summer of 1986, Airdrie made an approach for McGrain to become their player-manager. Negotiations reached an advanced stage until a last-minute change of heart by the Airdrie board. McGrain remained at Celtic for a further year; playing regularly at the age of 36: he missed only two games in the second half of the season. He played his final game for Celtic on 9 May 1987, a league fixture away against Hearts.