Rangers full-back Steven Whittaker has undergone a hernia operation and is set to be sidelined for at least six weeks, the Scottish champions said today. Whittaker, who last played on Christmas Eve against St Mirren, is in line to miss the Premier League games against St Johnstone, Aberdeen, Hibernian, Dunfermline, Kilmarnock and, possibly, Inverness. He could also be doubtful for the Scottish Cup tie against Dundee United at Ibrox on 5 February. Whittaker may be fit in time for Scotland\'s match away to Slovenia on 29 February but it is unlikely he will be risked in an international friendly, with the home league match against Hearts on 3 March more of a realistic target. Rangers have further injury concerns, with replacement full-back Kirk Broadfoot facing a scan on a knee problem. The Ibrox club are currently two points behind league leaders and arch-rivals Celtic.