The Arsenal left back will miss 4-6 weeks, not 3.
Now the reasoning behind bringing forward the transfer of Nacho Monreal is made clear. Instead of missing just 3 weeks with a thigh strain, Arsene Wenger said today that the England full-back will be absent for 4-6 weeks, and, worryingly, "could easily become 8 weeks before he is full back". Gibbs' injury is a "grade two thigh strain", which WebMD tells me
will lead to infection, amputation and cancer is a moderate loss of function after a significant number of fibres are torn.
This means Gibbs is probably out for both legs of the Champions League tie against Bayern Munich, which means Andre Santos still has a "key role" in the Arsenal squad. Hopefully, given his recent defensive performances, that key role is as backup for Lukas Podolski, which is something that the wandering Brazilian might actually be good at. But as long as Nacho Monreal and Thomas Vermaelen are fit, Santos should be nowhere near left back.
Meanwhile, let's hope Kieran Gibbs returns quickly. I for one am excited about the left-back battle; genuine options is always a nice thing to have.