By Editor Wayne Veysey

During a season-and-a-half of generally supreme performances in an Arsenal jersey, one truism has been that when Alexis Sanchez is fit, he starts.

Indeed, even when the ultra-committed Chilean has not been fit, he has still started. He is that good.

Turning matches, and winning them, Sanchez has been the go-to man when a goal is needed. Until now.

For the first time in his Arsenal career, it is questionable whether the 27-year-old should be the nailed-on starter that has previously been his undisputed right.

Since returning a month ago following an eight-week lay-off Sanchez has looked off the pace. Everything – his touch, passing, that famous burst of acceleration – has been out of sync.

With pivotal matches in the coming week against Barcelona and Manchester United, Sanchez’s form is a growing concern to Arsene Wenger and his staff. The red hot Chilean’s powers have seemingly been frozen.

In six matches since returning to the team, he has scored just once, in the FA Cup against Championship side Burnley, but it is his performances that will have the Arsenal coaches fretting.

Introduced as a second-half substitute against Hull on Saturday, Sanchez’s cameo was a microcosm of his last month. He frequently lost possession and his shooting was either too slow or mis-cued.

He was willing – he always is – but one of the team’s three genuinely world-class operators (Mesut Ozil and Petr Cech are the other two) was no more the answer to Arsenal’s failure to capitalise on their possession than any of his second-string team-mates.

For fixtures that will define their season, Arsenal need Sanchez back to his best. If not, should Wenger think what was once the unthinkable and consider demoting the forward to the bench?

Alexis Sanchez is back in full training ahead of Arsenal's clash against Chelsea

Sanchez has struggled since returning from a two-month lay-off

Danny Welbeck was used in the left-flank role against Hull and followed up his fairytale return against Leicester with an impressive display of athleticism and power. With Theo Walcott, Alex Oxlade-Chamberlain and Joel Campbell all fit and available, there is finally competition for attacking places in Wenger’s team.

With Olivier Giroud primed to spearhead the attack against Barcelona and United, and Ozil scheming in the spaces behind him, there is the opportunity for Wenger to be creative with the other two positions.

Sanchez has looked a shadow of the player who was once in total mastery of English football but the likelihood is that Wenger will put his trust in the forward who scored 47 goals in 141 appearances for Barca.

Welbeck is unlikely to be promoted so quickly for a fixture of such intensity, although he could come into the reckoning for the trip to former club Old Trafford. None of Walcott, Oxlade-Chamberlain or Campbell are in top form, and are most likely playing for one place.

Wenger will trust Sanchez’s raw speed will return, along with the touch and penetration in the final third. Arsenal could struggle to break down their opponents without it.