I don't think there's any need to rush him right now. I would imagine he was licking his lips to be able to be able to come on in a game Arsenal were absolutely dominating on Saturday and help, finally, push a very ragged Leicester over the cliff. There's a world of difference between that game state and one you'd typically find from minute 1 of your average Premier League fixture.
But what I think is super exciting is, not only was he trusted to come on and be that difference on Saturday, but he was that difference.