Arsenal manager Arsene Wenger found himself attacked from all sides on Wednesday after his selection decisions backfired to leave his team facing an embarrassing group-stage exit in the Champions League.

Wenger elected to pick David Ospina instead of first-choice goalkeeper Petr Cech at home to Olympiakos on Tuesday, but the Colombian committed a first-half howler, palming a corner into his own net, as Arsenal lost 3-2 to register a second consecutive Group F defeat.

"OOPSPINA" was the headline in British newspaper the Daily Mirror, while the Daily Express said the former Nice goalkeeper had committed a "calamity" and The Sun said Wenger's men had been "humiliated".

Wenger claimed afterwards that Cech had been left on the bench due to a "slight (fitness) alert" prior to Saturday's 5-2 win at Leicester City, but Arsenal great Ian Wright said the Frenchman had made a "big mistake".

"For somebody who's not playing often -- and this is a must-win game -- how can you put Ospina in goal? You've got to question the manager there," Wright, Arsenal's second-highest all-time goal-scorer, said on BT Sport.

"I think that's a big mistake. Why not start with Petr Cech, simply because of the experience he's got? Because we have to win this game. Arsenal have to win this game."

Cech, an £11 million ($16.7 million, 14.9 million euros) signing from Chelsea, was Wenger's only close-season recruit and the calamitous cost of rotation in the Champions League has revealed serious shortcomings in Arsenal's squad.

Wenger made six changes for the group opener, a 2-1 defeat at unheralded Dinamo Zagreb, and five for Tuesday's game, which saw Olympiakos prevail on English soil for the first time after 12 consecutive defeats.

Arsenal may have shared the back page of The Sun with Chelsea -- beaten 2-1 at Porto -- beneath the banner "EURO TRASH", but whereas the Premier League champions' trip to Portugal represented their toughest Group G assignment, Arsenal's biggest battles are still to come.

Their next group fixtures are a double-header against Pep Guardiola's formidable Bayern Munich, in-form Robert Lewandowski and all, who eliminated Arsenal in the last 16 in both 2013 and 2014.

Should Arsenal fail to win at least one of those games, they will face elimination at the group stage for the first time since 1998.

"Normally we're out by the quarter-final, last 16," added Wright. "This time we've got a massive hill to climb."

Wenger has built his reputation on his success in establishing Arsenal as Champions League perennials, leading them to the competition's group stage 18 times in succession and to the knockout phase for the past 15 seasons.

But their record in recent years has been one of diminishing returns. They were beaten finalists in 2006 and semi-finalists in 2009, but have gone out in the last 16 for the last five seasons in a row.

Paradoxically, Arsenal fared better in the Champions League when Wenger's ability to invest in new players was hindered by the cost of the Emirates Stadium.

Now free to splurge money on global stars like Mesut Ozil and Alexis Sanchez, Arsenal curiously look more vulnerable than ever.

Echoing last season's fatal 3-1 loss at home to Monaco in the last 16, the defeat by Olympiakos highlighted what have become habitual failings for Wenger's men, who have lost six of their last 12 Champions League home games.

Ospina's blunder was the latest in a long line of avoidable individual errors that have hurt Arsenal in Europe, while Alfred Finnbogason's 66th-minute winner arrived just a minute after Sanchez had equalised.

"The Ospina mistake and conceding the third goal like they did is a disaster," said former Arsenal defender Martin Keown.

"I can't remember a more disappointing European result for Arsenal."

To compound matters, Arsenal lost Laurent Koscielny to a hamstring injury in the second half, weakening them yet further ahead of Sunday's home game against Premier League leaders Manchester United.