Arsenal winger Bukayo Saka has been ruled out for "many weeks" after tearing his hamstring.
Saka limped off in the 24th minute of Arsenal's game at Crystal Palace on Saturday and while the Gunners went on to win 5-1, the victory was marred by the injury to the England winger, who left the stadium on crutches.
"It's not looking good, he's going to be out for many weeks," Arteta said in a press conference on Monday.
"I cannot be too specific because I do not know but it's going to be many weeks.
"He was gutted. You can tell that he's not been injured because he's been really emotional and down and we have to lift him up. It's a part of his job, a big part of his job. He will be fine, but he needs a few days."
Asked about the blow of losing Saka, Arteta replied: "It's a huge one, he's a massive player for us.
"You have to see the impact he has on this team but it will be a good exercise for all of us to overcome another challenge, because we've had a lot in the season."
It is not the first hamstring injury Saka has suffered this season. He limped off while on England duty in October and was sidelined for a few weeks, missing Arsenal's 2-0 loss to Bournemouth.
Asked if Saka's season could be over, Arteta said: "No. In football, with injuries you cannot put 10 fingers there but I am very optimistic that he will be well back before the end of the season."
Arsenal still beat Crystal Palace without Saka, with Gabriel Jesus scoring twice and Gabriel Martinelli - who moved to the right wing after Saka went off - claiming a goal and an assist.
"Gabi [Jesus] has played there [on the right], Ethan [Nwaneri] has played there, Leo [Trossard] has played there, Kai [Havertz] can play there, asking him to do different things. We will try and speak to them as well," said Arteta.
"I'm putting some ideas together, I haven't got there yet. But I have a few and then I want to speak with them to understand how we're going to generate that and take it in a positive way. That is going to mean we're going to be different."
The loss of Saka has been compounded by an injury sustained by Raheem Sterling in training.
Arteta confirmed the on-loan Chelsea winger will also be absent for a while.
"He's going to be out for weeks, I believe," added Arteta. "He needs some further testing. It's his knee, we will have to see in 24 hours but unfortunately he is going to be out for a while."
With both of his two first-choice options at right wing out injured, Arteta was then asked if Arsenal will move in the January transfer window regarding that position.
"We'll have to look internally at what we have and be creative," he said. "Do a very good exercise again, how can we mould the squad and adapt to the circumstances?
"And be different. We cannot pretend to be the same, we have to be different and find the best way to do it, be competitive and win a lot of games.
"My intention right now is within the team and what we have, get the best out of that.
"You might be right: somebody could come in and score 40 goals. What we have is what we have and I am happy with what we have, they fully try to do everything that we demand. We have enough quality in the squad. How we use it? That's something else.
"Preparation is done, we are ready if something happens. We didn't predict the situation with Bukayo and Raheem [being out] at the same time. At the same time, we predicted for something more to happen in the defensive line, but the job is done.
"Then ok, if something has to happen, we will be open to it. But the main focus is now how do we have the structure still with the potential in this squad?"
Sky Sports' Sam Blitz:
Saka's injury is massive news for Arsenal. The England winger's injury history has been impeccable and Arteta speaks regularly about how consistency and availability are his biggest attributes.
Since making his Premier League debut in 2019, Saka has never missed back-to-back Premier League games due to injury. In the past two-and-a-half seasons, Saka has only missed four top-flight games.
Whenever he has picked up a knock, he bounces straight back - so for Arteta's Arsenal to lose him until February is brand new territory.
It is a major blow given how reliant Arsenal are on Saka's work down the right-hand side. The Gunners attack down the right 46 per cent of the time - it is the highest percentage for one flank in the Premier League this season - partly due to Saka and Martin Odegaard venturing to that side.
So how do Arsenal respond, especially with Sterling - the player brought in as cover for Saka over the summer - also set for a period on the sidelines?
The next player in line is Gabriel Martinelli, who stood in for Saka at Crystal Palace on the right wing. The Brazilian also started on the right for Arsenal's win over Everton on the final day of last season, the only game Saka missed for the whole of last term.
Gabriel Jesus is another option for the right wing, with Arteta using the forward on the flank before, but Arsenal's No 9 has just found some form through the middle again. Now is not the time to move Jesus around again.
So what Arsenal need to work with now is a weakened right-hand side and a left-hand side which has failed to impress this season. It is time for Martinelli and Leandro Trossard to step up.
And there is the option of the January transfer window. Arsenal's previous stance with regards to the market was they would only move if a long-term transfer target becomes available - or if injuries force their hand. With Marcus Rashford looking for a new challenge, it may be a tempting option...
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