Arsenal have been dealt a major blow after new £31.6million signing Mikel Merino suffered a shoulder injury in his first training session with the team.

Merino suffered a suspected fractured shoulder in a training session on Thursday and Arsenal manager Mikel Arteta has confirmed the midfielder faces “weeks” out.

The midfielder had only completed his move from Real Sociedad on Tuesday and he would have hoped to make his Arsenal debut against Brighton on Saturday.

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But now Merino must wait and he is due to undergo further scans as Arsenal seek to learn the full extent of his injury.

“Very unfortunate,” said Arteta. “Yesterday he had a collision and he has a shoulder injury unfortunately. It looks like he’s going to be out for a few weeks.

“First session. He was really excited and everything was looking really good. He landed on the floor and Gabi [Magalhaes] landed on top of him and it looks like he has a small fracture probably.

“We have to see [how long he will be out]. He was in so much pain. We’ll have to do some more tests on that and then we’ll have more conclusive answers.”

Mikel Arteta on Takehiro Tomiyasu injury

Arsenal will also be without Gabriel Jesus for Saturday’s game against Brighton after he picked up a groin injury last week.

The Brazilian is “progressing really well” in his recovery, though, and should not be set for a long time on the sidelines.

“He is progressing really well,” said Arteta. “He had a little muscle injury and he is doing quite a lot of stuff already, so we expect him to be with us pretty soon.”

Takehiro Tomiyasu will also be absent from the squad for the match with Brighton at Emirates Stadium due to a knee injury.

The Japan international has not played any matches in pre-season and Arteta could not confirm when he will be back.

“At the moment, it’s difficult to say,” he said. “It’s a bit slow the process of the first phase of that injury. It’s probably for the medical team to say more on that.”