Arsenal fear that striker Olivier Giroud will be out with an ankle injury until the new year, leaving manager Arsène Wenger preparing a move for Manchester United's Danny Welbeck in the final few days of the transfer window.
Giroud was last night undergoing tests on a suspected broken ankle sustained in the 2-2 draw at Everton on Saturday, but Arsenal are braced for the worst, which would rule out their main centre-forward for the rest of the year.
Wenger was coy at yesterday's pre-match press conference for the Champions League qualifier at home to Besiktas tonight and said he was waiting for "further investigation" of Giroud's injury to his tibia and, adding that he was "not in the mode to be [talking] about buying or selling".
However, it is now almost inconceivable that Arsenal will not seek reinforcements before the transfer window closes on Monday night.
Arsenal have a long-standing interest in Welbeck, whom Louis van Gaal would be willing to part with.
Welbeck would be open to joining but United are very reluctant to sell him to a main rival, especially after Arsenal blocked their move for Thomas Vermaelen. They would therefore demand up to £16m for the 23-year-old England international. Arsenal's current valuation is thought to be closer to £12m.
Arsenal, meanwhile, find themselves with far too much on the line against Besiktas at the Emirates this evening, knowing that they need to win.
The Champions League play-off match is a more lucrative game than any that will be played for the next nine months, guaranteeing £25m for participation in the group stage.
Arsenal have played at that stage for the last 16 years and, as Wenger made clear yesterday, the prestige at stake matters at least as much as the money.
"For us it is very important," he said.
"We want to play at the top level, at international level, so it is a very important game. More on the sporting side than the financial side. The task is clear, and we know we can do it. So let's do it."
Arsenal's task, of course, is to win. Their 0-0 draw in Istanbul last week means that a score draw would knock them out, and they know that they have to play better this evening than they did at the Olympic Stadium, on Istanbul's western outskirts.
"It was one of our first games this season so the technical side of our game can improve from that performance," admitted Alex Oxlade-Chamberlain, likely to be drafted into midfield this evening to fill the gaps left by Aaron Ramsey and Mikel Arteta.
"It was a tough pitch to play on, but no excuses. We should have passed the ball better than we did. We have to improve the speed at which we move the ball. The fluidity wasn't at the highest. It wasn't a terrible performance, but we are capable of more."
The problem is that Arsenal will have to do more with less. Arteta is missing due towith an ankle injury sustained after a heavy tackle from Demba Ba in Istanbul last week.
Ramsey is suspended after picking up two bookings as Arsenal tried to stem the tide in the first leg. Those are Arsenal's two most important midfielders and the team certainly looks less solid without them.