Arsène Wenger believes Jack Wilshere will be sidelined for four weeks with an ankle injury and confirmed that Alexis Sánchez is set to miss Arsenal’s opening game of the Premier League season against West Ham on Sunday.

Arsenal will begin their league campaign without Wilshere, who is also at risk of missing England’s Euro 2016 qualifiers against San Marino and Switzerland next month after sustaining a hairline crack of his left fibula in training.

Sánchez returned to training this week after a break following his successful Copa América with Chile. The South American will not play at the Emirates this weekend but is expected to return in 10 days.

On Wilshere’s injury, Wenger said: “It’s bad luck, purely accidental. It’s a hairline crack in his fibula. It’s in the region where they took the screws off so I believe it’s a straightforward bone injury, which means there’s no surprise there. He just needs time to heal. The news he got yesterday was that it could be much shorter than expected because he’s two weeks in a boot and then maybe after that he can practice straight away again.

“You never get used to that. When you play football you never get used to your body letting you down. The positive thing in this injury is that it’s not a recurrence of one of his former injuries. The positive news with Jack is that the history doesn’t play a big part in his head when he comes back. He plays with the same confidence and desire as before. It’s difficult. We have all been at that age when you love to play football, and when you cannot get up in the morning and play it’s mentally difficult.”

On Sánchez , the Arsenal manager added: “He came back in surprisingly good shape. I will see. Sunday will certainly come too early but in 10 days he should be alright. Will he not be involved at all on Sunday? I don’t know yet. It depends a little bit on what I see tomorrow and who will be available. He understands that perfectly well. He is one of the players who played the World Cup, came back here and played the whole season without a break, goes to the Copa América and basically cannot start the season.”

Wenger confirmed that the 20-year-old midfielder Serge Gnabry will join West Bromwich Albion on loan, having passed a medical on Thursday.