Manchester United top the table from local rivals City by the virtue of goal difference while third-place Arsenal's draw at Wigan cost them the chance to go level on 38 points with both Manchester teams.
Diaby's initial injury problems began in September following a challenge by Bolton defender Paul Robinson.
The Arsenal midfielder then went on to miss nine weeks because of an ankle problem after appearing in the 2-1 home win against Birmingham on 16 October.
Diaby has only made nine appearances for the north Londoners this season in the league, scoring once in August.
He secured a move to the Gunners in 2006 from French side Auxerre for £2m.
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