After victory over Catania yesterday, Mourinho conceded: "When we go into the Champions League and play at a faster tempo and greater intensity, some of the players struggle a little.
"This will give me pause for thought in future when choosing my line-ups and I'll put a bit more focus on Europe.
"I cannot say if I will rotate the squad consistently. Tonight we knew [Ivan] Cordoba was ready to play and [Walter] Samuel needed a rest. The same goes for [Patrick] Vieira and [Dejan] Stankovic. We may well change again with Palermo, but at the moment we don't have the squad to do a proper rotation."
Wesley Sneijder curled in a free kick for his second goal of the campaign.
"I do not ask more from him, just that he keeps his position and plays the ball, bringing creativity rather than worrying about the defensive moves. His timing, passing and vision are great, he is a very important player for us."