In his post-match press conference, Arsene Wenger confirmed that left back Kieran Gibbs would be out for 3 weeks after picking up a thigh strain around the 30 minute mark. Annoyingly, the injury came after he strained to get to a pass that was made for an offside player, Andre Wisdom, but under new offside rules, the flag wasn't raised. Gibbs tried playing on, but clearly couldn't use his left leg, and thus made way for Andre Santos, raising the blood pressure of the watching Arsenal fans.
Santos played one of his better games this season, which resulted in being out-muscled by Jordan Henderson for the second Liverpool goal, and nearly throwing away the point by passing straight to Luis Suarez in the second half. He also was seemingly playing defensive midfield at points in the second half. However, he wasn't blown away by Stewart Downing, so that's one positive.
Not only is it a defensive loss, with Gibbs one of the better defenders in the team (meaning he's vaguely competent), but it's also an attacking loss. Gibbs' attacking runs down the left have been a major side of Arsenal's attacking game, and his partnership with Lukas Podolski is extremely important. Without that, Arsenal can sometimes be a bit blunted.
So, get well soon, Kieran. Meanwhile, Arsene, in the remaining 24 hours of the transfer window, you might want to get a left back.