I said this a few games ago, that Lewis still needs to learn his craft in 'lesser graded' games before pushing for first team proper. At the time, I said I classed Arsenal in the top tier of games he shouldn't play in yet(okay, this was the FA Cup, so almost acceptable).
Whilst he wasn't terrible, I didn't think he was effective and Walker could have easily played there all game. Martinelli would have tore him a new one as he gave Walker issues.
Anyway, I was told the other week "if he's good enough, he's old enough". Yes and no. In a straight game, for a straight team, I'd see that. This team is never a straight one under Guardiola's expansive tactics.
The kid's good, but he needs time.