It was a clash of personalities: Mathieu Flamini, the artisan workhorse, and Mesut Özil, the mercurial maverick.
The flashpoint came in the dying embers of Arsenal's Champions League defeat to Bayern Munich, when the scoreline was still 0-1. Flamini was furious Özil, not the most dilligent of defenders, struggled to track back and allowed Bayern a shot at goal. He physically rebuked his teammate, who angrily shrugged him off.
This wasn't on the same level of Graeme Le Saux and David Batty, let alone Kieron Dyer and Lee Bowyer's punch-up, but the exchange was a unique insight into £42.5 million Özil's mindset.
His saved penalty was, Arsène Wenger accepted, due to his "style of play". Few Arsenal supporters would have retained confidence in the German when he executed that ominous stutter before nonchalantly clipping the ball down the middle, only to see it beaten away by Manuel Neuer. Özil's been in England less than six months and has already inherited the nation's penalty-taking skills.
Özil remonstrates with Flamini late on
"I think he wanted to do so well tonight and that affected him," Wenger added. "You could see even five or 10 minutes later on the pitch he was shaking his head and it had a huge impact on his performance."
That failure contributed to Özil's reaction to Flamini's stinging advice, however, this is not the first time his on-pitch behaviour has been questioned. In December, he was confronted by Per Mertesacker as he headed for the tunnel - rather than the section of Arsenal supporters - following their 6-3 defeat at Manchester City. He apologised for not acknowledging the supporters later on, but at Anfield earlier this month, he again refused to acknowledge them fans when he was substituted in the 5-1 humiliation.
Although these are inconsequential details, they matter, especially to a support as success-starved as Arsenal's. Özil's irritable acts have come during a 14-match goal drought which has stretched over the last 10-and-a-half weeks, and this is not a coincidence. His winter dip has become a slump, despite two spirited displays against Manchester United and Liverpool last week, and even Wenger is "concerned" by his record signing's confidence.
With Arsenal just a point behind Premier League leaders Chelsea, Wenger faces another selection quandary. Olivier Giroud has looked laboured since the turn of the year, and his off-pitch indiscretion has coincided with his demotion to the substitutes' bench at the expense of Yaya Sanogo. Now Özil looks mentally, if not physically, tired.
He was behind only Flamini and Jack Wilshere in terms of ground covered on Wednesday night (he ran 11.69km), and Wenger almost certainly would have taken him off had events not conspired against him. Kieran Gibbs' injury and Wojciech Szczęsny's red card enforced two first-half substitutions, while Alex Oxlade-Chamberlain was also hurt before the break and was eventually withdrawn.
Özil has featured in all but one game this year and even started against Coventry City in the FA Cup. He was regularly substituted by José Mourinho during his three years with Real Madrid and Arsenal have reportedly put him on a weight programme. A joy to watch in full flight, he is too lightweight.
Mesut Özil
Eden Hazard, who Mourinho has moulded into one of the best attackers in the world, has usurped Özil and is now the Arsenal playmaker's yardstick. The Belgian has expanded on an auspicious debut season at Stamford Bridge and is a more disciplined forward who Mourinho can rely on to muck in. Özil has shown flickers of defensive discipline recently.
Sunderland visit the Emirates on Saturday and, with no midweek game until the return leg with Bayern on 8 March, it is an opportune time to drop Özil, who looks in need of a 10-day rest, ahead of the trip to Stoke and the FA Cup quarter-final with Everton.
Joe Hart benefitted from his belated relegation to the bench after a woeful year between the sticks for Manchester City, and has not made a mistake since his return in December. If Arsenal are to lift silver this season, Özil cannot afford any more mistakes, either.