Arsenal's Tomiyasu out for season after knee surgery
The 26-year-old Japan international has made just one appearance since suffering the injury, which he sustained in pre-season.
The Gunners have endured several injury setbacks during the current campaign, with Kai Havertz and Gabriel Jesus both out for the season, and Bukayo Saka and Gabriel Martinelli sidelined at the moment.
"Takehiro Tomiyasu has undergone a successful surgery on the right knee issue which he first sustained in pre-season," said an Arsenal statement.
"Despite an initial surgical procedure in August, followed by a return to full training, and featuring as a substitute in our home Premier League match against Southampton in October, Tomi continued to have issues with his knee, resulting in a further corrective surgical procedure.
"Tomi will now begin his recovery and rehabilitation programme, which is expected to be completed towards the end of this year."
Tomiyasu, in an Instagram post, said: "I had surgery on my knee a few days ago and I've already started my rehab to do what I love the most again.
"It has been the toughest period in my career for sure and it carries on a bit more but I won't give up. Thank you for your support and see you soon at the stadium."
Arsenal are second in the Premier League, seven points behind leaders Liverpool, and they next play London rivals West Ham at the Emirates on Saturday.