Arsenal midfielder Alex Oxlade-Chamberlain will be “out for a while” according to Arsene Wenger.
The England international limped out of the Gunners' opening day 3-1 defeat to Aston Villa with serious concerns over the extent of the injury.
Reports have suggested the 20-year-old could be out for as long as six months, and speaking today, Wenger failed to put a timescale on Oxlade-Chamberlain's return.
"The difference from Saturday is that Oxlade-Chamberlain is out for a while with a knee problem," Wenger said on Arsenal Player.
There was, though, better news on Bacary Sagna, Kieran Gibbs, Aaron Ramsey, Jack Wilshere and Tomas Rosicky, all of whom trained on Tuesday morning, as did defender Nacho Monreal, who has been out with a back problem.
There had been fears over the fitness of those individuals, especially full-back Sagna, who landed awkwardly towards the end of the game on Saturday, but they could all play some part in Turkey as Arsenal look to seal a place in the lucrative group stages of the Champions League.
"Everybody else should make it. There's a final decision (on Wednesday) but Sagna and Gibbs should be available," said Wenger.
"Nacho Monreal is back and will travel."
Wenger admitted following Saturday's defeat, when his side were booed off the pitch at full-time, how the players respond will shape their season.
Taking on Fenerbahce in the Sukru Saracoglu Stadium will certainly prove a test of character, but Wenger is confident it is one which Arsenal can pass.
He added: "Yes of course (they are the most important games of the season). We fought very hard last season to be in the top four and that game has a vital importance.
"It is a consequence of what we tried to achieve last season and therefore, on the back of our defeat against Aston Villa, it's important as well to bounce back straight away.
"To be part of the top level - that is for us the most important thing. All the rest are the consequences of it. When you are a football player, you want to play at the top level and that's what the Champions League is about."
Arsenal defeated Bayern Munich away last season, with the Germans going on to win the tournament, and in the 2008/2009 campaign the Gunners beat Fenerbahce 5-2, which ended the Turkish side's impressive 15-match unbeaten home run in Europe.
Wenger said: "We try to win everywhere we go. That is the only target we have to set ourselves.
"We respect Fenerbahce highly but in the history of our club we have gone everywhere, all over, and always had a desire to win and that is what we will do again."
If Arsenal do reach the group stages there will be even more calls for new faces in north London, after a bid for Newcastle midfielder Yohan Cabaye was rejected on Monday.
The £10million move for the France international is the latest failed transfer attempt during a frustrating summer for Wenger, who has also looked at signing the likes of Wayne Rooney, Luis Suarez and Gonzalo Higuain with no success to date.
The Gunners fans were vocal during the Villa game, chanting "spend some money", as Arsenal are understood to be sitting on a £70million warchest with which to try and attract marquee names to help mount a long-overdue sustained title challenge.