Arsenal have announced that Mikel Arteta has undergone surgery to his left ankle, and will be out for approximately three months. The news follows reports that Arteta faced a lengthy layoff due to a setback. Arteta's original injury, a calf problem, occurred in the 2-0 victory against Borussia Dortmund in late November, but Arteta had been expected to return in December. Arsène Wenger confirmed that Arteta suffered a setback with a related ankle problem, but that was expected to only keep him out until the beginning of this month.
Instead, Arteta has had surgery to remove a bony spur that had caused inflammation. The period that he is out, 3 months, means that Arteta is facing a battle to be available for the final month of the season, and means that Arsenal are likely to play Matheiu Flamini or Francis Coquelin instead. The difference is quite obvious: Coquelin and Flamini are good tacklers, but their positional intelligence is far below that of Arteta, and their lack of ability on the ball means that Arsenal's passing game is far harder to carry out, especially against opposition that press, as was seen in the 2-2 draw with Liverpool and 2-0 loss against Southampton.
For all of the drum-banging about Arsenal needing a new defensive midfielder, buying a player of Arteta's quality in January is quite difficult, and while there are some possible loan options, they are not long-term options. A longer-term option, such as Morgan Schneiderlin, is unlikely to happen until the summer.