Arsenal fans had plenty of what-ifs during Arsene Wenger 's time in charge, but the one which produces the most soul-searching concerns Abou Diaby's fitness.
The French midfielder saw his early career derailed by a horror tackle which prompted Wenger to raise the possibility of legal action, and he would later suffer a number of further setbacks - big and small - before retiring at the age of 32.
He expressed his sadness at people bringing up his injuries and suggesting he was made of glass after being restricted to just 214 career appearances.
Diaby's injury record is the kind of thing which is frustrating for any player, but it feels worse to some thanks to the quality he showed during those spells between the injuries. There were a few great displays to choose from, but perhaps none more impressive than his performance in a Champions League win away at Fenerbahce in 2008.
Arsenal had begun the 2008-09 season without Diaby, a thigh injury keeping him on the sidelines until October. A late cameo against Everton brought an assist for Theo Walcott, and Wenger decided the then-22-year-old was ready to be thrown straight in as the Gunners travelled to Turkey.
Fenerbahce didn't look like the easiest opponents on paper. They had won all six of their home fixtures in the previous season's Champions League, getting past Anderlecht in a play-off and denying Inter Milan, PSV Eindhoven, CSKA Moscow and Sevilla at Sukru Saracoglu Stadium and even defeating eventual finalists Chelsea at home before the Blues turned things around at Stamford Bridge.
In total, their unbeaten home run in Europe was into double-figures when they welcomes Arsenal to Istanbul. That would soon end in style, though, and Diaby would be a big part of that.
How good would Abou Diaby have been without his injuries? Have your say in the comments section
A frantic first half saw the Gunners open up a 3-1 lead inside half an hour. Emmanuel Adebayor and Theo Walcott took advantage of an open home defence to put Wenger's side two to the good, and - after a Mikael Silvestre own goal - it was Diaby who restored the advantage.
The midfielder got to a ball through the middle before defender Edu Dracena, but still had work to do. Not that he was in any mood to make things look difficult.
As the Brazilian centre back floundered and eventually fell to the turf as if trying to hide from the inevitable, the Arsenal man calmly strolled forward and fired a low shot under goalkeeper Volkan Demirel.
Further goals in the second half from Alex Song and Aaron Ramsey - either side of Dani Guiza breaking the offside trap to score - rounded off an easy victory. After the game, though, it was Diaby who came in for the most praise from his manager.
"He can play nearly everywhere, Diaby," Wenger said after the game, as reported by Goal. "From midfield going forward, he can play everywhere.
"He has been out for nearly three months now. It was his first start and he had a very good game."
Diaby stayed relatively injury-free for most of the rest of the campaign, and indeed for the following season. He only missed a few more games after returning in 2008, suffering an abdominal problem later in the season, and he added goals against Aston Villa, Newcaslte and Stoke in the Premier League.
The Newcastle goal was a classic example of what he could do going forward, and added fuel to Wenger's comments. He strode through the Magpies' defence, ignoring challenges from more than one angle to the point that it looked like he simply had more time to work with than the defenders, before firing high into Steve Harper's net.
The 2009-10 campaign was Diaby's best yet, with seven goals and - perhaps more tellingly - 40 appearances. However, the injury issues would soon return and he only played another 42 games in total for Arsenal before leaving in 2015.
In 2016, Diaby told the Mail on Sunday he considered that 2006 challenge from Sunderland's Dan Smith as the source of his injury troubles, but said he had moved on. "There is no resentment any more. I left it behind a long time ago," he said.
"The only thing I wish is that it had happened later in my career. If it happened when I was 28, things might have been different. Between 19 and 27, I would have had time to progress, play every week and be the player I should have been."
If you need an idea of the player Abou Diaby should have been, as he puts it, you could do worse than seek out the performance at Fenerbahce in 2008. Arsene Wenger could see the quality, and he wasn't exactly the worst judge.
