Arsenal lost for the seventh time this season last night and it was not all Emmanuel Eboué’s fault. The Ivory Coast defender was targeted for abuse by his own supporters in the victory over Wigan Athletic at the Emirates Stadium at the weekend, but Arsenal played so poorly against the Portuguese champions last night that real questions have to be asked again about whether Arsène Wenger’s team have the strength in depth to avoid a fourth successive season without silverware.

Wenger may have put out a scratch side against Porto, but what must worry the Frenchman is that many of the established players who were selected looked out of form — in the case of William Gallas, an accident waiting to happen. With Arsenal already two goals down — a result that consigns them to second place in group G and a possible last-16 tie against Barcelona, Bayern Munich or Juventus — the former Arsenal captain made defensive mistakes the likes of which would not look out of place on Hackney Marshes. Come back Philippe Senderos, all is forgiven.

“Porto were stronger than us tonight,” Wenger said. “We didn’t underperform. Underperform is a big word. When we were 2-0 down, the belief was not there. We were not strong enough to come back.”

The Champions League group stage has failed to provide many thrills and spills this year and this was another game that did not excite the imagination in the early stages. Both teams had already qualified for the first knockout round, so there was little at stake apart from the honour of finishing top of the group.

No team have reached the final after finishing second in their group in the past three seasons, but Arsenal have hardly had the luck of the draw in recent campaigns, regardless of where they have finished in their groups. In 2005-06, Wenger’s team finished top of group B and reached the final in Paris, but only after having to see off Real Madrid and Juventus.

Anyway, Wenger has little time for statistics or omens. The Frenchman was unaware that he was taking charge of Arsenal for the 700th time last night until it was pointed it out to him and, even then, his only reaction was to comment that every one of the 124 defeats — now 125 — that he had endured during 12 years in North London had caused him “terrible pain”.

With one eye on the Barclays Premier League match away to Middlesbrough at lunchtime on Saturday and owing to a lengthy injury list, Wenger was without nine first-team players, including Cesc Fàbregas, the captain, Emmanuel Adebayor and Robin van Persie. Adebayor and Van Persie scored twice each in the 4-0 defeat of Porto at the Emirates in September, so it was left to Nicklas Bendtner, looking ridiculous in lime-green boots, to lead the line as a lone attacker.

The main point of the exercise as far as Wenger was concerned was the rehabilitation of Eboué, who started at right back four days after he was reduced to tears by his own supporters. “He got the support of the fans tonight and he did all right,” Wenger said.

“It will take time for him to recover.”

Arsenal’s 1,500 travelling supporters greeted the defender before kick-off with a few choruses of “There’s Only One Emmanuel Eboué” and all was going well for the 25-year-old until the seventh minute when he conceded a free kick on the edge of the penalty for a clumsy foul on Givanildo Vieira de Souza, the Brazilian forward also known as Hulk, who was Porto’s most dangerous player in the first half.

Eboué was standing out for all the wrong reasons two minutes later when he gave the ball away cheaply in Porto’s half, but to be fair to him, the home team had identified him as the weak link in the Arsenal defence and he received little help from Aaron Ramsey in front of him in midfield as Hulk, Cristián Rodríguez and Lucho González took it in turns to attack the point of least resistance.

Not that Eboué was at fault when Porto scored after 37 minutes. Abou Diaby was the guilty party, allowing Bruno Alves to beat him in the air to head down a corner taken by Raul Meireles past Manuel Almunia in the Arsenal goal.

Eboué struggled, too, at the start of the second half, when he was booked for another clumsy foul on Rodríguez and there was a suspicion that he played Porto’s attackers onside when the home team extended their lead two minutes later through Lisandro López. A clever pass by Fernando caught out Mikaël Silvestre, playing at left back, and López gave Almunia no chance with a stunning right-foot strike that flew past the Spanish goalkeeper.

Ten minutes later, Eboué was in trouble again when Rodríguez went close to making it 3-0. The former Benfica forward accelerated past the Arsenal right back, but was kicking a post seconds later after he dragged his low-left foot strike wide of the target.

“Everyone wearing an Arsenal shirt has to give 100 per cent,” Almunia, the captain last night, said after the match. “That was not the case tonight.”

Porto (4-3-3): Helton — Fucile, Rolando, B Alves, P Emanuel — L González, Fernando, R Meireles — L López (sub: T Costa, 78min), Hulk (sub: F Guarín, 88), C Rodríguez (sub: Mariano, 78). Substitutes not used: Nuno, M Stepanov, Lino, T Sektioui. Booked: González.

Arsenal (4-1-4-1): M Almunia — E Eboué, W Gallas, J Djourou, M Silvestre — A Song (sub: M Randall, 79) — A Ramsey (sub: J Wilshere, 59), Denilson, A Diaby (sub: K Gibbs, 59), C Vela — N Bendtner. Substitutes not used: L Fabianski, G Hoyte, F Merida, J Simpson. Booked: Eboué.

Referee: K Vassaras (Greece).