Juventus are closing in on yet another Italian title, seven points clear at the top of Serie A with eight games to play.
“Tomorrow’s a difficult game for us,” Sarri said.
“Milan, who have already created problems for us this season, are in great physical and mental condition and are playing at high levels.
“At a time like this, the mental aspect is very delicate and mistakes are only around the corner. The lads know it’s going to be a tough month, so they can’t lose focus.
“Our lead at the top shouldn’t make us relax. We’re at a time when games are all difficult and messing one up is extremely easy.
“We’re just focusing on tomorrow’s game. We’re not even looking at who we’re facing next.
“I haven’t made any [personnel] decisions yet. We’ll see what happens, but the obvious solutions seem to be Rugani and Higuain.
“Everyone’s been talking about how big our squad is, but right now we don’t have that many options to choose from.
“Chiellini and Alex Sandro had their first proper training sessions yesterday. Higuain’s getting better. He’s training non-stop now and mentally he’s ready.”