Arsenal midfielder Thomas Partey will miss the "next few matches" after suffering an injury in Sunday's north London derby defeat at Tottenham, says boss Mikel Arteta.
Partey had been out for almost a month with a thigh problem before being selected to start Sunday's 2-0 loss, but was unable to complete the game after picking up another injury.
Arteta said it was not a recurrence of the same injury and defended his handling of the Ghana international's return, insisting he had not been rushed back ahead of schedule to face Spurs.
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"He got injured in the same area, but not in exactly the same spot as before," Arteta said ahead of Thursday's Europa League group game against Dundalk.
"He had an MRI yesterday, there is an injury there, he will miss the next few matches."
Asked if it was an unnecessary risk to rush him back from injury, Arteta said: "No, he did incredibly well, he was confident. We tested him three times and he had no symptoms.
"But in football you have a lot of unpredictable actions. He went into the floor, his knee got stuck, after he needs to stretch and get up up. Immediately he put a lot of stress in a similar area and he felt it again."
Arteta had been critical of Partey for refusing to play on through injury during the defeat at Spurs after he left the field injured in the build-up to their rivals' crucial second goal.
After Heung-Min Son's stunning long-range strike had given Spurs the lead on the counter at the Tottenham Hotspur Stadium, Arsenal were hit by another break in first-half stoppage time as the injured Partey vacated midfield and allowed Harry Kane to double the lead.
Arteta was seen attempting to push Partey back onto the field moments before Kane rifled Spurs into an insurmountable lead, and the Gunners boss admitted his player was in the wrong to leave the pitch.
"Thomas is out, he's limping, he's in pain, he has to come off and we lost a man in that crucial transition moment," Arteta told Sky Sports. "He has to fall on the floor.
"I wanted him on the pitch, doing whatever he could for the team in that situation. No one expected him not to be in that position."
Speaking in his post-match press conference, Arteta added: "I was trying to push him back on the pitch, I don't think he realised the gravity of the situation when he left his position."
'No one is undroppable - not even Auba'
Arteta insists even captain Pierre-Emerick Aubameyang is not guaranteed a place in his team as he looks to get the Gunners back to winning ways.
Aubameyang has not travelled with the squad for Thursday's Europa League dead-rubber against Dundalk, with Arsenal are already assured of top spot in Group B having won their opening five matches of the campaign.
But it is domestically where Arteta is struggling to find a solution to a poor run of form and a run of lacklustre performances. One of the main problems has been a lack of goals, only the current bottom three have scored fewer than Arsenal's 10 so far, with Aubameyang not scoring from open play in the league since the opening weekend.
Arteta said he was not tempted to take his skipper to Dundalk in an attempt to play him into form and that his recent blip does not mean he has an automatic place in his Premier League XI.
"No one is undroppable at the end of the day," he said.
"You have to find the right players to win football matches but we cannot forget what Auba has done for this club and what he's done in recent months - not years ago.
"And as well because I see how he is training, how he is behaving and how much he wants to turn the situation around.
"When I see that type of hunger I stay as a strong supporter to a player when he is established in the team and the performances that he has provided.
"Listen, today and this week, the response I have seen from the players and the reaction I saw from the players after the match, I cannot be any prouder.
"Auba was one of the main guys there and today he was walking the place with an energy that wouldn't be associated to a team or a player that is suffering at the moment and this is for me the way we have to approach it."