Despite splashing out on Mesut Özil, Arsenal supporters' groups have called for further significant investment over the next two transfer windows after the club's financial results revealed they are still sitting on a large cash pile.

The club's results to the end of May 2013, which do not take into account their summer transfer dealings, show that the club had £153.5m in the bank.

Even taking the £42.5m signing of Özil into account and the reserves required to fund the business, the Arsenal Supporters' Trust believes Arsène Wenger should have up to £80m to spend over the next two transfer windows. That financial firepower is underlined by the expected contribution of new commercial deals with Emirates and a new kit supplier (expected to be Puma), the full effects of which will not be seen until this financial year.

Previously Arsenal's earning power was depressed by the long-term deals signed to underwrite the move to the Emirates. The accounts show that pre-tax profits were down to £6.7m from £36.6m the previous year, largely as a result of a smaller profit on player trading, despite the sale of Robin van Persie to Manchester United and a £10m one-off impairment charge on writing down the value of players.

They also show an 8% uplift in the wage bill to £153.5m. But on the plus side they also reflect increased turnover of £242.8m, up from £235.3m last year, largely as a result of the first benefits of the new £150m deal with Emirates to sponsor their shirts and stadium. Arsenal's chairman, Sir Chips Keswick, talked up the signing of Özil – calling him "one of the world's best players" – but said the club would continue to follow a prudent course.

"It is my job to ensure we steer further along the course we have set," he said. "We must continue to grow commercially to provide the club with the best opportunity to achieve success and we must do this in a way which remains true to our values and which ensures and protects the long-term sustainability of the club."

He underlined, however, that significant sums remained available for Wenger to spend, if he deemed it necessary. "With the Özil transfer I believe we have made a significant statement and when Arsène decides the time is right to invest again Stan Kroenke, myself and the rest of the board will be delighted to support him."

The Arsenal Supporters' Trust, which has consistently called for more investment in the playing squad, said it believed the 2012-13 results would represent "the last year of Arsenal selling its best players to achieve profitability as the substantial increases in revenue from both renewed TV contracts and commercial deals come on stream".

"We are encouraged that since the season ended much progress has been made by Arsenal to remove the non-performing players from the wage bill. This pruning has allowed scope for more concentrated wage spend," said an AST spokesman.

"Looking forward, Arsenal are in a healthy financial position, with substantial cash reserves. The AST continues to urge the club to invest the money it has to further strengthen the current first-team squad and improve the chances of winning silverware. Substantial funds are available for additional transfer and wage spend without affecting self-sustainability."

Keswick also underlined the board's confidence in Wenger, whose contract expires at the end of the season. "We have a manager in Arsène who is as focused and determined to win trophies as he was when he first arrived," said the Arsenal chairman, who took over from Peter Hill-Wood in June