Manchester United's cash reserves fell by £100m in six months, in part to finance an investment in the squad attempting to win the fight for domestic supremacy with Manchester City.

After spending which included stadium improvements and a bond repurchase programme, the club's bank balance dropped from £150.6m to £50.9m to 31 December of last year, the club's quarterly accounts revealed yesterday.

Despite net spending of £48m on new players, including the goalkeeper David de Gea, defender Phil Jones and winger Ashley Young, United have fallen out of three cup competitions, including the Champions League, and trail City in the Premier League.

United spent £5.3m in the three months to 31 December buying back bonds, issued two years ago, to raise £504m to replace long-term financing and reduce debts to hedge funds.

United have now spent £92.8m repurchasing that debt – more than the £80m received from Real Madrid in 2009 for the sale of Cristiano Ronaldo. The club's debt, resulting from the 2005 takeover by the American Glazer family, stood at £439m at the end of 2011 and incurred almost £24.5m in interest payments in six months. Although the debt was down from £508m at the end of 2010, it rose again in the final three months of 2011 by £6m.

However, United's money-making abilities appear undiminished, with £175m generated in six months to the end of December – up more than 10 per cent on the same period a year earlier thanks largely to rises in TV income and a new training kit sponsorship deal with DHL.

"Revenues continue to grow strongly, although costs are increasing just as quickly, so pretty much negating that growth," the Manchester United Supporters' Trust said in a statement. "However the key figures of interest to supporters show the Glazers have now spent every penny of the money received from the sale of Ronaldo, and more. That's now £92.8m spent on buying back their own bond debt that they loaded on to our club."

Meanwhile, the United defender Rio Ferdinand wants to win the Europa League – if only to shut a few kids up in the school playground. Now a father to three children, Lorenz, Tate and Tia, Ferdinand has discovered that his status as a United player does not spare him from the cutting comments that are so much a part of school life.

"You have to understand, we've still got lives to lead outside of football," he said. "When you're walking up the path to school, you don't want little kids laughing at you or making fun of you because you've been beaten.

"That's what happens if you lose games or get knocked out of competitions. Young kids can be unforgiving. There's nothing in their minds that goes: 'He plays football, leave him alone'. If anything, they're even worse for it.

"And there's still a little kid inside me who has pride and an ego and wants to make sure I can walk up that path and nobody can say anything to me because we've won."