Arsenal get surprise injury boost for Chelsea derby as Mikel Arteta issues three-man update

The Gunners face their toughest test of the season so far as they take on Xabi Alonso’s side, who have also won both of their opening two matches.Timber is yet to feature this season after undergoing minor surgery over the summer, and was not expected to return until later in September.However, the Dutchmanhas stepped up his training and will be assessed against of kick-off."He's in really good condition at the moment,” Arteta said of Timber. “He's been on the pitch for a few weeks and he’s been training with us now, so he's in a good place."Asked if Timber could face Chelsea on Sunday, Arteta said: "We will decide again tomorrow after training." Bruno GuimaraesGettyBruno Guimaraes is expected to be fit, despite not being seen in first-team training on Thursday.His workload continues to be managed but Arteta confirmed at his pre-match press conference that Guimaraes was set to be involved for the London derby.Arteta said: “He had a knock against Villa in the previous game. He's being assessed, but probably tomorrow he will be OK to train." Declan Rice is also fit and available, despite coming off in the second-half at Villa Park.However, there is more uncertainty over Cristhian Mosquera, who has not been in training after he picked up an issue against Villa.Read MoreArteta said: ”It was more precaution than anything else. We will have to see tomorrow in the session how he feels." If Mosquera misses out, Ezri Konsa is likely to slot in at centre-back, with Arteta confirming that the defender is available to start.