Injured Walcott out of Arsenal squad
The winger fell awkwardly following a challenge from Michael Dawson during Arsenal's 5-2 victory over Tottenham on Saturday but was able to complete the match after receiving treatment.
Arsene Wenger has confirmed the 23-year-old will be sidelined for the 'short term' and will subsequently sit out Arsenal's tie against the French champions at the Emirates, while Andre Santos will also miss out through injury.
Wenger also revealed Kieran Gibbs and Gervinho are fit enough to be included in Arsenal's squad after recovering from injury.
With four games played in the Champions League, Arsenal sit second in Group B on seven points and trail leaders Schalke by a single point.
Olympiakos are third having won two and lost two so far, while Montpellier are yet to register a victory but secured a draw against Schalke last month.
Meanwhile, Thierry Henry will train with Arsenal next month and could return for a third spell as a player at the club, Goal.com can reveal.
The club's all-time leading goalscorer has been told by the club he can keep in shape at their London Colney training base during the MLS off-season.
Wenger wants to strengthen his squad with a striker in January and has made Atletico Madrid’s Adrian Lopez his top target.
However, if Arsenal cannot clinch a deal for the Spain international, they are considering turning once again to Henry, who has just completed his third season at New York Red Bulls.
The Londoners will lose Gervinho on Africa Cup of Nations duty in January for up to six weeks and doubt surrounds the future of Walcott, even though progress has been made in his contract negotiations with the club.
The Frenchman, who turned 35 in August, had a fairytale seven-match return to Emirates Stadium at the start of the year, extending his Arsenal scoring record to 228 goals.
The striker returned to London last week after New York Red Bulls were beaten in the MLS play-offs to end their domestic campaign.
The Frenchman now plans to go on holiday before coming back to London in December.
The former France international capped an excellent season for New York Red Bulls, which yielded 15 goals in 29 games, by being one of the three players nominated for the MLS most valuable player of the year award.
Graham Zusi of Sporting Kansas City and the San Jose Earthquakes striker Chris Wondolowski are the other nominees.