My big buys will pay off soon, insists Wenger

In a depressing season for Arsenal to date, the few reasons for cheerfulness have mainly been derived from the Champions' League.

Whether on the touchline or banished to the stand, Arsène Wenger has observed two good wins in the critical qualifying round over Udinese, who then shot to the top of Serie A; a draw in the Borussia Dortmund bearpit that only felt anti-climatic because the home side scored in the final minute; and a 2-1 home victory against Olympiakos which should have been more convincing after running up a two-goal lead in 20 minutes.

In three different competitions over the next 10 days, Arsenal must attempt to transfer their European form to the domestic arena as they play winnable home games against Sunderland (this afternoon), Stoke (next Sunday) and Bolton (in the Carling Cup on Tuesday week) on either side of Wednesday's trip to Marseille.

Wenger believes they can go on a run, despite injuries to key players such as Jack Wilshere and his only experienced right-back, Bacary Sagna, who broke an ankle in the demoralising defeat by Tottenham last time out. "I do," he said, "[Jose] Santos is a good player, [Mikel] Arteta is a very good player, [Per] Mertesacker for me is getting stronger in every single game. [Ju Young] Park is getting stronger and has just come back from Korea, where he scored three goals in two games. They only arrived one month ago basically, you know."

Even those supporters calling for reinforcements over the summer would not have wanted quite such a turnover. Wilshere's ankle operation, coming on top of the departures of Cesc Fabregas and Samir Nasri, has devastated the midfield, which was the team's strength. Alex Song, there to give it some beef, has been forced into the back-line alongside Mertesacker, who was getting used to playing next to Laurent Koscielny when he was injured too.

Some have found Mertesacker a disappointment, his height not counting for as much as it should and his pace suspect, but Wenger insists it is too early to be passing judgement. "I like him. He is getting more aggressive, is a very intelligent player and will be a big asset. He's not the quickest but uses his brain well. Trust the Germans, they can fight! You know what it is like, if you don't win, nobody is [any] good but the players who are mentally strong get over that and I think he is.

"People judge your buys quickly but I am happy with the buys we made. I've heard that Song is a bad buy, that [Thierry] Henry is a bad buy and over time they were not so bad. I'm not happy with the results but that is completely different."

It would appear to be a good time to be playing Sunderland and an interesting one to meet Marseille, whose season mirrors Arsenal's: poor in domestic competition, much better in Europe, where they won at Olympiakos, then drubbed Dortmund 3-0. "That was a complete surprise to me because I was impressed by Dortmund," Wenger said.

"Marseille are good on counter-attack. The two games against them will decide our qualification. If we take four points, we will qualify. It's as simple as that."

Arsenal v Sunderland is on Sky Sports 1 today, kick-off 1.30pm