Nick Train, co-founder of London-based funds boutique Lindsell Train, has spent five years building a 5.2% stake in Celtic's ordinary shares, and the house has also bought some preference shares issued by the club for its portfolios.
He told The Herald: "We would never have invested in Celtic if it had had the sort of debt one knew was in Rangers.
"We met the management and we understood that the balance sheet was effectively debt-free and the philosophy of the major shareholder Dermot Desmond was to keep it debt free."
Mr Train has been quietly adding to his portfolio while, on the other side of Glasgow, Rangers has plunged into administration with estimated debts of £134 million.
Former Sheffield United chief executive Charles Green and Zeus Capital have bought the business and assets of Rangers but the club in its new company structure faces a future in the lower league after opposition to its readmission by other Scottish Premier League sides.
Mr Train said of his Celtic investment: "We have made a risky investment. But we have not taken a balance sheet risk as well."
Lindsell Train took its stake in Celtic, which only constitutes a tiny proportion of the funds he manages, because Mr Train believes the development of new media platforms could massively widen the audience for sports and push up the value of sports franchises.
He noted the recent purchase of the LA Dodgers baseball club for $2 billion (£1.3bn) by a group of investors including legendary former player "Magic" Johnson.
That was the largest transaction yet for a professional sports club.
He also highlighted the £731m takeover of Arsenal football club by American businessman Stan Kroenke and the £300m takeover of Liverpool of Fenway Sports Group.
The valuation of football clubs will come under further scrutiny in the coming weeks after Manchester United revealed plans for a $100m listing in New York. It had previously considered an initial public offering in Hong Kong or Singapore.
Mr Train, whose funds include the £215m Finsbury Growth & Income Trust, suggested that recent deals imply that Celtic is undervalued.
"This is a quite irreplaceable global brand. Celtic is followed worldwide as a result of the diaspora of Scottish people and Irish Catholics.
"There is a very substantial following on the East Coast of the United States."
"If Fenway is right and Liverpool football club is worth £300m, if Stan Kroenke is right and Arsenal is worth £700m, how can Celtic be worth only £30m?
"It just seems wrong, However, maybe it will never change."
Celtic already has links with the highest levels of the City by virtue of BT chief executive Ian Livingston's seat on its board.
Mr Train said: "I have looked at a lot of quoted football clubs. Ninety-nine out of 100 I wouldn't touch."
Lindsell Train is now the fourth-largest shareholder in Celtic behind Mr Desmond, an Irish businessman, Christopher Trainer, owner of Glasgow-based advertising company Forrest Group and 6.6% shareholder James Keane, according to Reuters data.
Mr Train specialises in targeting companies that successfully manage brands and has longstanding holdings in companies including AG Barr, which produces Irn-Bru, as well as Johnnie Walker whisky owner Diageo.
He has tipped the technology and media sectors for strong growth in the coming years.