Arsene Wenger wants to find the cause of the injury crisis that is threatening to derail Arsenal's season.
Theo Walcott will miss the rest of the campaign with a ruptured cruciate ligament in his knee, while Aaron Ramsey has not featured since picking up a thigh injury on Boxing Day.
Jack Wilshere fractured a bone in his foot during England's friendly win over Denmark, while Mesut Ozil could be out for up to six weeks with a hamstring injury suffered against Bayern Munich on Tuesday.
All four are out of Sunday's crucial North London derby clash with Tottenham as the Gunners look to breathe life into a faltering title challenge, and Wenger acknowledges the injuries are a worry.
"I am concerned that this happens," he told reporters. "If you look at our overall injury list going into such a decisive part of the season, we have not Wilshere, not Walcott, not Ozil, not Ramsey and we went to Bayern without [Kieran] Gibbs and [Nacho] Monreal.
"We are analyzing very deeply why it happened and to see if there is a link between all these injuries. For Walcott, it's completely bad luck. Wilshere — I don't think it is linked with the other injuries; it's more linked with his history and the kick he got.
"But the rest, maybe we have to find why it happened. It's very difficult to find any obvious reason why. For example, a player like Ozil — he was rested against Stoke, then he goes to Germany and he trains different, sometimes on a different ground with different sessions. He played the whole game [for Germany against Chile] and the whole game for us against Everton and he produced on that day, doing more physically than usually and he paid for it the next day. Why? I don't know."
Wenger said he is particularly concerned about Ramsey. The Welshman was Arsenal's star performer in the first half of the season but is still two weeks away from making a return.
"That's our worry at the moment, Ramsey is taking longer than expected," Wenger said. "He had a first setback and then he planned to join in [training] on Thursday but he had recurring pains in his thigh. Of course, he's now a little apprehensive because of the setback. We have to be very cautious with him. When will he be back? I believe it's two more weeks now."