According to an announcement posted on the London Stock Exchange, Sergeant bought 1.7 million shares on 24 January, increasing his holding to a little less than 4.8 million shares, or 7.4%.
Shares in Rangers were trading at 27.55p at 2.35pm, a gain of 1.1% on the day but well below their 52-week high of 88p. At that price Sergeant's stake is worth around £1.3 million.
The manager, who first bought a small stake in Rangers on its IPO in December 2012, said he had 'taken advantage of recent share price weakness', and that he saw 'long term value in the franchise'.
The purchase comes as former Rangers' director Dave King told the Daily Mail that a new share issue at the club was 'inevitable' and the company prepares to embark on a intensive cost-cutting programme.
'We are in for an interesting couple of months,’ King told the paper. ‘If [chief executive] Graham Wallace pushes these cuts through and gets his budget balanced – which he has to do because the money is not there – then how are the board going to be able to show the fans a way forward when it comes time to stump up for season tickets?
In the three years to 24 January the UK Equity Long Term Recovery and UK Equity High Alpha funds have returned 64.7% and 47.1% respectively versus a 28.5% rise in the FTSE All Share.