He will ask Alexis Sanchez why he took a penalty against Hull – and not designated spot-kick taker Santi Cazorla.
He said: “It was Santi Cazorla to take it, I don't know why it didn't happen.
“Did Santi not want to take it, or did Sanchez take the ball? We have a pecking order, but on the pitch they have to want to take it.
“But he was not planned, Sanchez.
“I want always to know what happened. And for it not to happen again, we have to see why that happened.
“But overall, anybody can miss a penalty. You have to accept that.
“It happens to all of us… and it's happened to Santi Cazorla as well."