It comes as a blow to Arsenal in what was otherwise an almost perfect evening in Yorkshire, as the Gunners thrashed Leeds 4-1 to cement their place in the top four.
Gabriel Martinelli grabbed a brace before Bukayo Saka made it 3-0 before half time, and Emile Smith Rowe came off the bench to add a fourth minutes after Raphinha pulled one back from the spot.
The win was slightly marred by the suspected injury of Tomiyasu, and another star is now ruled out as Covid cases surge once more.
Arteta had already confirmed before kick-off that Albert Sambi Lokonga had missed out after testing positive, and at full time the Spaniard confirmed that Pablo Mari would also be isolating.
Arsenal’s match against Leeds was the only game to take place on Saturday due to rising cases amongst the Premier League, and the Gunners followed Manchester United in shutting down their training ground to prioritise safety.
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When asked about his decision to temporarily close London Colney, Arteta said: “Pure precaution because we had some cases in the staff and we wanted to prevent any issues.
“Everybody we have seen around us, when they have a few cases the cases have risen.
We wanted to protect our people and Gary [O’Driscoll] and the medical staff made the right call, to try to close it for a day, stay away from the place, make sure that all the tests from everybody were negative and make sure that when we were back, everybody was safe.
“We had another player, as well Pablo has Covid, so unfortunately they [Mari and Lokonga] will be out.”
Another player Arsenal fans feared may be out for the near future was Tomiyasu, as he was substituted shortly after the hour mark following a knock sustained against Leeds, but Arteta gave an encouraging update.
“No it was more a muscular issue,” Arteta explained. “Obviously, he’s got a big load on him.
“He’s played every single minute since he joined us and even this week he’s been a little bit struggling. So we decided to take him off, he wasn’t 100% confident to continue in the game and hopefully he’s not injured.”
Tomiyasu has been excellent since making the £16million move from Serie A side Bologna on deadline day this summer, and the Japanese international has become a key member of Arteta’s back line, making the right-back position his own.
With a heavy festive period, precaution must be taken to keep players fit, so Arteta will be hoping that it is nothing serious, and that the defender will be back in action as soon as possible.