If Djourou is unavailable then William Gallas will presumably step in at centre back alongside Kolo Toure, with Justin Hoyte or Mathieu Flamini at left back. That'd be an interesting choice, with Wenger having said that Flamini doesn't like playing at left back and apparently being happy with it, but with Flamini surely looking the better bet what with the experience of last season's terrific run in Europe, when the defence set new records for the Champions League.

As for Freddie, it wouldn't be surprising if he started on the bench anyway, with Alexander Hleb and Tomas Rosicky taking to the wings in a 4-4-2 (I suspect that Wenger will use a 4 man midfield tonight but even if he goes for a 5, it could be Baptista rather than Freddie that takes the 5th spot).

Thierry Henry is said to be over his foot problem. Although he certainly didn't look to be over that problem for the first hour of Saturday's match, he went on to have a major part in all 3 goals, proving once again to the doubters that even a half-fit Henry can be a match-winner. Arsene Wenger has alluded to this and said that now he's had a whole match since the injury he should be sharper.

Philippe Senderos, Gael Clichy, Abou Diaby, and Lauren are all still unfit. Apart from that the only doubt is Theo Walcott who missed the Blades match with a shoulder injury picked up playing for the reserves last week.

Porto got off to a disappointing start on matchday 1 with a home nil-nil against CSKA Moscow, but they did have some of their better players missing so we have to warn against over-confidence. They're going well domestically at the moment, playing a 4-3-3 with an emphasis on defense but with some strong attacking players too.

One of those player to watch out for tonight is Postiga, the former Spurs striker who was a young flop in the Premiership but has developed well since returning to Portugal. He'll probably line up alongside Adriano up front.

They've also got a fine winger in Quaresma, who like Postiga had a disappointing spell abroad (at Barcelona) but has got himself back on track back in his homeland. There's also Anderson, a dangerous young Brazilian who's probably going to be on the bench to start with, but likely to be used if they find themselves needing more firepower.

They've got a few injuries in Joćo Paulo and Bruno Moraes (knees), Tomislav Sokota and Pedro Emanuel (achilles), and Ibson (foot). Diogo Valente and Paulo Ribeiro have apparently been left out of the squad. But Raul Meireles has recovered from a foot injury.

Arsenal have never played Porto before, which I guess is why many previews are banging on about a Highbury night in 1991 against another Portuguese side that, frankly, we'd rather not have to think about. So they're from Portugal... does that really make it relevant?