Arsenal are facing up to the prospect of being without the hugely influential Alexis Sánchez and Santi Cazorla for their decisive Champions League group game against Olympiakos next week, though initial assessments of Laurent Koscielny's fitness are more promising.

Sánchez departed the turf after an hour of Sunday’s draw at Norwich City having pulled up with hamstring trouble in his right leg.

The Chilean had felt tightness in the muscle after the midweek win over Dinamo Zagreb but the club's tests on the thigh had indicated he could play at Carrow Road, only for the forward to hobble off signalling to the bench that he had felt something tear.

One leg

Cazorla suffered a kick from Gary O’Neil on his left knee which appeared to jar the joint and ensured he played the second half, according to his manager, “on one leg”.

Arsenal will compile a more detailed assessment of both players’ injuries in the next 48 hours but already rate both players as serious doubts for the games against Sunderland and, more significantly, in Greece next Wednesday.

Arsenal need to beat Olympiakos by two goals – or 3-2, 4-3 and so on – to guarantee qualification for the knockout phase of the competition.

They have played the Greek team three times in final group matches since 2009 and lost them all, albeit they had already qualified on each occasion.

The news on Koscielny is far more encouraging despite Arsène Wenger having said post-match that the France centre-half “could not walk” after suffering a hip spasm eight minutes into the game.

That had led him to clutch at his lower back and depart the pitch after 11 minutes – he was replaced by Gabriel Paulista – to join an already lengthy list of walking wounded.

Yet, from those worrying early signs, the hope is Koscielny will return to training before the end of the week and should be in contention against Sunderland.

His availability would represent a boost with Arsenal, fourth in the Premier League table, saddled by a troubling injury list.

Hairline fracture

Before the draw at Norwich they were already without Kieran Gibbs (calf), Jack Wilshere (hairline fracture of his left leg), Danny Welbeck (knee), Theo Walcott (calf), Francis Coquelin (knee), Mikel Arteta (calf) and Tomas Rosicky (knee). The hope is Walcott is closest to a first-team return, potentially this weekend. Guardian Service