Arsenal’s hopes of securing a 16th straight season in the Champions League knockout phase are now hanging by a thread after Tuesday's calamitous home defeat to Olympiakos that piled fresh pressure upon manager Arsene Wenger. Already under scrutiny for Arsenal’s failure to sign a single outfield player in the summer transfer window, the way events unfolded at the Emirates Stadium brought renewed criticism.

The Arsenal boss elected to leave the one player he did sign over the summer, Petr Cech, on the bench and watched on as replacement David Ospina spilled a corner into his own net during the 3-2 defeat. The result leaves Arsenal without a point from two Champions League matches.

Despite now being one of the world’s richest clubs, Arsenal have struggled to go that extra step and truly compete for Premier League and Champions League titles in the past decade. And now staring at a group-stage exit from Europe’s premier competition, Wenger can expect further calls for him to invest in the squad in the January transfer window.

It was strikers that the Gunners were linked most keenly with this summer, and that may well prove the case again leading into the next window. Already stories have begun about the future of possible target Alexandre Lacazette. The France striker was in high demand after firing 27 Ligue 1 goals for Lyon last season, but he appeared to end the speculation by penning an extension to his contract in the summer. Yet the 24-year-old has now revealed he was left disappointed by the way Jean Michel Aulas made the negotiations over his new deal public.

“It hurt,” he told French publication L’Equipe, per the Daily Mail. “I think that is a justified word to use. When you are a youngster at the club, in the town, and you have never really behaved in a nasty way to anyone, to be treated like that, yes, it hurts. I had had my best ever season, I really helped the team to reach the Champions League again.”

The comments come amid a tough start to the season for Lacazette, in which he has been jeered by his own supporters and scored just once in eight appearances. While a move in January is still unlikely, the situation should certainly encourage Arsenal.

Arguably another weakness in Arsenal’s squad is their lack of depth in the defensive midfield position. Highly rated Portugal international William Carvalho has long been suggested as a player who is being targeted to fill that void, but the Gunners could face serious competition for the Sporting Lisbon man’s signature.

Italian outlet Tutto Mercato Web claims that Chelsea, Paris Saint-Germain and Liverpool are all keen on the 23-year-old, who was elected player of the tournament at this summer’s European Under-21 Championship.

Given the way Arsenal defended against Olympiakos, a new central defender may also be under consideration at the Emirates Stadium. Indeed, in the past week there have been rumors that a £13-million January approach is being lined up for Juventus’ Daniele Rugani. After two impressive seasons at Empoli on a co-ownership agreement, Juventus purchased the player outright earlier this year. However, the 21-year-old has yet to feature for the Italian champions this season. While Italian website Calcio Mercato reports that Juventus are hugely reluctant to let Rugani leave, Arsenal are thought to be continuing their interest by sending scouts to watch him in action for Italy Under-21s earlier this month.

Finally, the Daily Mirror has reported that Arsenal are one of the clubs monitoring Bayer Leverkusen midfielder Hakan Calhanoglu. The Turkey international, who was signed from Hamburg in 2014, is renowned for his free kicks, and he has already netted five this campaign. Calhanoglu, 21, has also been linked with Manchester United and Italian giants AC Milan.