i dont know, it may be powerfull, but when in the Mange sharingan itachi controls everything. EVERYTHING. i mean he could just create a mountain ans sqush the fox a thousand times over. or he could create two foxes to fight the one. i dont think theres any limit to the power as its all inside his head. but to clarify that i doubt itachi could do that to the fox in the real world but when he is subdued by naruto i think it woudl be possible.