I mentioned it earlier, but he's looked really fatigued the last 4-6 weeks in Serie A, and against Monaco. This is his first season of top flight football playing significant minutes. I mean he's played over 2000' now, as opposed to 973' for Madrid last year. He had that amazing run through January-early March and Dortmund 2nd leg, but since then he's looked burnt out and unfit.
Allegri has only started him in 1 of the last 8 Serie A matches, he's come on as a sub in 5 of them, just to keep him game-ready, but I really think Allegri has been trying to allow him to recover from this fatigue, by hardly using him in Serie A. And it showed today. He was the player from the Dortmund matches again. Looked like he had boundless energy.