He isn't going to stand around while Naruto gathers NE, so if they were to meet up unexpectedly, then Naruto wouldn't have time to gather NE, thus not being able to enter SM.
Also, Sasuke Vs SM Naruto without the Kyuubi's assisstance equals Naruto easily being defeated by Genjutsu. The Kyuubi was his only counter against High Level Genjutsu. Hebi Sasuke had a 4 in Genjutsu in the databook, MS Sasuke should be higher since he has more power ofcourse.
To give Naruto a chance, we would have to give him the advantage of starting off the battle in SM. After 2 RS Naruto's Senjutsu chakra runs out, meaning no SM, & he can't enter it again im battle cause his opponent isn't going to stand around and let him gather NE, besides that, he can only make an additional 3 clones whilst in Sage Mode (if he has 2 off the battlefield prepped in SM).
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Needs two clones in order to make a RS.
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After 2 RS, he runs out of Senjutsu chakra.
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3 clones
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Sasuke is fast enough to dodge RS, or he could block it with Susano'o which Should be able to handle it considering just it's ribcage was able to defend him against A's Liger Bomb, which Darui said no one ever survived, & an Imperfect Susano'o tank Gaara, Temari, Darui, & Kankuro's simultaneous attacks at the same time. At the very most it would take a Full Susano'o to counter RS.
