West Ham midfielder Jack Collison admits he's been shocked by his progress this season.
"I was a little bit shocked and then he's called me over and said 'you're going on'. I didn't have much time to think. I just had to stick my shirt on and I was on the pitch.
"He told me to get close to [Cesc] Fabregas and try and stop them playing but obviously when you come to Arsenal, a team like that has got so much movement and interchanges. It is hard but I did my best."
He added: "It was a little bit of a shock to be involved.
"The gaffer told me earlier at the hotel so I had a little bit of time to prepare but I didn't expect to come on in the first half. It is just a dream really to come on at the Emirates."