Arsenal manager Mikel Arteta has admitted that he is unsure of the severity of Takehiro Tomiyasu's injury after the defender came off in their 1-0 win over FC Zurich in the Europa League.
Having just learned that he would be representing Japan at the 2022 World Cup, Tomiyasu took his place on the bench for the visit of the Swiss champions to the Emirates Stadium.
Kieran Tierney was given the nod at left-back instead, and the Scotsman's sweetly-struck half volley after 17 minutes was all it took for Arsenal to get the job done in North London.
Having managed to survive a nervy finale, Arsenal ensured that they would finish top of Group A and advance directly to the last 16, avoiding a playoff tie with a third-placed Champions League side.
However, the occasion was soured when Tomiyasu - brought on as a second-half substitute for Ben White - had to be withdrawn himself with an apparent leg issue in the dying embers of the game.
The 23-year-old has endured a frustrating time with injuries since joining from Bologna last summer, but Arteta currently has no indication of the seriousness of his latest problem.
Speaking to reporters in his post-game press conference, Arteta said: "We don't know. Obviously he felt something and we didn't want to take any risks.
"With the amount of games we are playing, it's part of [it]. It can happen in training, it can happen in games and unfortunately it happened to Tomi today. The rest all have to be ready because we're going to need everybody now."
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Tomiyasu has been a regular Premier League starter at left-back in recent weeks, but Oleksandr Zinchenko was back on the bench for the visit of Zurich and will be aiming to return to the first XI for Sunday's clash with Chelsea.
Tierney put in an impressive shift at left-back on Thursday, but Gabriel Jesus missed another gilt-edged chance to score early in the second half as his goalless streak stretched to eight matches in all tournaments.
However, Arteta is not fretting over the Brazilian's recent drought, adding: "That's going to change. He's getting the situations, he's getting the chances, he's contributing to the team an awful lot.
"He's helping to win matches. The way he competes for every ball and every single action is incredible. It will come. He needs to be patient, he's been through that in the past, and he needs to learn those lessons."
Arsenal had opened the door for PSV Eindhoven to overtake them on the final day after losing 2-0 in the Netherlands last week, and the Dutch outfit beat Bodo/Glimt to give themselves the best chance of advancing as group winners.
The Gunners needed to match or better PSV's result on the final matchday to remain at the summit, and Arteta was pleased with the reaction of his side following that loss, saying: "That's what we wanted.
"Losing football matches is part of it, it will happen at certain stages, you have to react to that. Analyse what happened and try to be better as a team. That's what we've done and now we have to go to Stamford Bridge."
Arsenal will now aim to maintain or extend their two-point lead at the top of the Premier League table in the weekend's London derby with Chelsea.
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