Lacklustre defence, Ozil at the heart of Arsenal's Round of 16 struggles

Arsenal were thrashed 5-1 by Bayern Munich on Wednesday for the second straight time in Champions League play, last losing to them by the same scoreline in November of 2015 in Group Stage play.

But things have not changed all that much since that last 5-1 loss under manager Arsene Wenger. New faces, same story.

Here are five ways Arsenal has struggled over the past year, despite new players and new tactics.

Round of 16 struggles

Arsenal has continued to lose in the Round of 16 in devastating fashion. In each of the last six Round of 16 first legs, the Gunners have lost, allowing 3+ goals in four of those six matches.

No team in European Cup knockout history has ever come back from a losing its first leg by 4+ goals so Arsenal have it all to do in the return leg at the Emirates on March 7th.

Ozil and Arsenal shrink in big games

Whether it is his fault or not, Mesut Ozil has not "shown up" in big games this season, creating 14 chances and no assists against the big teams this season in all competitions.

Against Chelsea, Man United, Tottenham, Man City, Liverpool, Bayern Munich and PSG, Arsenal have won just one of nine matches, and have been outscored by a score of 19-14.

Against these same seven clubs, Ozil is completing just 43.5 passes per game and creating 1.67 chances per game; compared to 58.1 passes and 2.93 chances per game versus everyone else.

Should Giroud Start?

Wenger has also not decided to play Olivier Giroud as a starter despite him having his most clinical season to date. In league and Champions League play, Giroud has converted 10 of his 14 shots on target for a conversion percentage of 71 percent, nearly twice as prolific as last season's rate of 39 percent.

By not starting Giroud as his lead striker, Alexis Sanchez has been used as Arsenal's lead striker more often than not and has thrived to the tune of 20 goals and 13 assists. However, it has had a negative effect on Ozil's playmaking.

Missing in Action

It is not entirely Wenger's fault that Arsenal has struggled in big matches, as his players also fail to show up in these types of matches. Against Bayern, it was Francis Coquelin. With Aaron Ramsey and Santi Cazorla out, Wenger relied on the French midfielder. Coquelin registered the second-fewest touches among starting outfield players, with Laurent Koscielny (injury) the only player with fewer, despite playing in a holding midfield role. Against Bayern, Coquelin was poor, completing just 44 percent of his passes and registering just 20 touches.

Lacklustre defence

Wenger also still has not solved the problem of his defense from a systematic perspective. Wenger did purchase centre-back Shkrodan Mustafi (from Valencia), who has developed a solid partnership with Laurent Koscielny. However, teams are scoring much more efficiently on Arsenal this season than in year's past. Teams are converting 44 percent of their shots on target in league and UCL play, highest rate allowed by Arsenal over the last seven seasons and a 12 percent increase from last season.