Celtic's recent dominance on the pitch has been mirrored by their financial results from the boardroom. In football, one doesn't simply follow the other - but it helps. They have avoided racking up huge debts to secure their silverware. It has come through financial prudence and a business plan based on two key areas: player trading and participation in European competition. Both have contributed hugely to Celtic's success. Player trading success looks simple on paper – make more money from selling than you spend on buying and continue to have success at the same time. It's an equation with so many variables, that few clubs crack the code. Celtic shifted their approach to player trading around 2004. Their basic principle was to prioritise the signing of young players under the age of 24. According to the football statistics site Transfermarkt, since season 2011-2012, Celtic have spent around £213m on players and have brought in around £260m. In only four of those seasons has the club spent more on players than it made selling. Success stories include the sale on Matt O'Riley to Brighton & Hove Albion for around £25m, Jota to Al-Ittihad for £25m and Kieran Tierney to Arsenal for £23m. Selling big players and re-investing sensibly until the next one comes along has been the key. Compare the Glasgow club's record to that of Manchester City, who made profit in player trading in just one of those seasons and made an overall loss on player sales of more than £1bn. Celtic are by no means the most successful club in Europe when it comes to player trading. Portuguese club Benfica, for example, have made a profit nearing £640m in player trading over the past 10 years, but successful player trading has become more than just a financial fall back for Celtic when they cannot rely on the riches of the Champions League.