Mikel Arteta has been ruled out for the remainder of the season with ankle ligament damage, leaving Arsène Wenger with selection issues in midfield for the derby against Chelsea at the Emirates Stadium on Saturday.

Yossi Benayoun, who is on loan from Stamford Bridge, is ineligible to face his parent club and, with Jack Wilshere out for the season and Abou Diaby short of full fitness, despite taking part in a training ground friendly against Oman on Wednesday, Wenger has little scope for manoeuvre.

Aaron Ramsey is expected to come in for Arteta alongside Alex Song, with Tomas Rosicky continuing in the No10 role and Alex Oxlade-Chamberlain or Gervinho starting on the left. Wenger has to hope that Diaby will be fit enough for the substitutes' bench or his options will be restricted in a game that he described as "massive and vital".

Its importance has been heightened in the wake of Arsenal's shock 2-1 home defeat by Wigan Athletic on Monday night. Were Arsenal to lose to Chelsea, they would surrender control of their destiny in terms of a Champions League finish, with Tottenham Hotspur and Newcastle United in a position to overhaul them. No one at Arsenal can countenance that, particularly after their Premier League revival which began in February.

Going into the Wigan game, they had won nine out of 10 matches in the competition, with the blip coming in the 2-1 defeat at Queens Park Rangers. Yet they were second best against Wigan – their defending was dismal; their attacking game flat in the second half – and the injury to Arteta added to the frustration.

The Spanish midfielder rolled his ankle when crossing a ball in the early running and he was forced off. Because there was no stoppage in play Arsenal were temporarily reduced to 10 men and Wigan took full advantage by scoring their second goal. Wenger grumbled about that afterwards but his fears over Arteta's fitness have been realised.

The scans revealed no break and the ligament damage in the ankle continues to be assessed. But it is already known to be serious enough to rule Arteta out for the final weeks of the season when, after Chelsea, Arsenal play Stoke City, Norwich City and West Bromwich Albion.

Arteta was signed from Everton for £10m moments before last summer's transfer window closed and he has been something of an unsung hero, winning Wenger's praise and trust for his technical assurance, composure and consistency. The 30-year-old has contributed six Premier League goals for the club, the most eye-catching of which was the late winner against Manchester City earlier in the month.

His influence in the dressing-room has also been important and André Santos, who joined Arsenal from Fenerbahce at the same time as Arteta, credits him with helping him to settle. "Our languages are quite similar," said the Brazil left-back, "so he is helping me the most. He is always giving me instructions about the Premier League as he played for Everton for a long time … We're always messing around in the changing room, on the pitch during the warm-up. He's always saying something to make me laugh or calling me nicknames but it's always good-spirited."

Santos, who scored in Arsenal's 5-3 win at Chelsea last October, is fighting to retain his place for the return fixture ahead of Kieran Gibbs, who was an unused substitute against Wigan. Santos endured a difficult evening on Monday. Laurent Koscielny will return in the centre of defence after a two-game ban.

Diaby, who has endured a nightmarish season with injury, played for 45 minutes against Paul Le Guen's Oman, as Arsenal won 1-0 but Wenger is conscious of rushing him into the first team, having done so at Liverpool on 3 March and seen him break down.