Arsene Wenger insists Arsenal will still be a force to be reckoned with after Alex Song was confirmed as the latest key player to leave the Emirates Stadium.

Song's departure to Barcelona came minutes after the final whistle of the 0-0 draw against Sunderland on the opening day of the Premier League season on Saturday.

His transfer comes as Wenger attempts to cope with star striker Robin van Persie's move to Manchester United on the eve of the campaign starting.

Arsenal's lacklustre efforts without van Persie and Song, who was left out of the squad for the Sunderland clash, suggests Wenger's side face a major struggle to end their seven-year trophy drought.

But Wenger believes his squad already has enough strength in depth to cope with the changes, while he could also make another signing before the transfer window closes on August 31.

When asked about Song, Wenger said: "He expressed a desire to leave for Barcelona. "It is frustrating but we have learnt to deal with that. I also believe the financial potential of some clubs is massive and that makes a difference.

"But Jack Wilshere is coming back now in one or two months. We have Abou Diaby coming back, we have (Tomas) Rosicky not far away and might get a midfielder in as well."

Olivier Giroud came on for his debut against Sunderland and shot wide with Arsenal's best chance, while Lukas Podolski did not get a clear-cut opportunity on his first appearance as Arsenal laboured to unlock Sunderland's stubborn defence.

"Overall we lacked something in the sharpness, the quality and accuracy in the final pass," Wenger said.

"The formula did not work with three strikers and we were not well balanced and didn't create enough.

"They locked our midfield and after that it was difficult for us. We need to be more creative."

Santi Cazorla's debut, however, pleased Wenger. The Spaniard created Arsenal's best chances and went close himself.

"It's difficult not to be pleased with him. He played the whole international game in midweek and he basically created all the chances," Wenger said.

Speaking about his new signings, Wenger added: "I never denied we lost a world-class player and that he's difficult to replace.

"Podolski is not ready yet but he has the quality, Giroud has the presence when he is on the pitch.

"But of course Manchester United bought Robin van Persie at 29 years of age as that quality is not easy to find on the market."

Meanwhile, Sunderland boss Martin O'Neill was delighted with his side's performance after a frustrating summer in the transfer market.

O'Neill has been able to sign only two players -- Carlos Cuellar and Louis Saha -- but he took heart from the way his team frustrated Arsenal with an obdurate display.

"We have been unable to get the squad to strength but that game will bring us on immensely," he said.

"I knew coming here was going to be difficult. We ran out of energy towards the end and we were hanging on, but at least we are off the mark.

"We should have done better in the first half, James McClean had a shot and Jack Colback got himself into a good position too, but in the second half Arsenal had most of the possession and we had to defend."