Italy has only 2 tanks to start with not counting Africa so those two tanks are all you have to worry about. They may send their bomber for help but their force must be fast to keep up with the German stack. What you need to do is predict where Germany wants to move the stack next and then put at least 2-3 units there to prevent Italy from taking it. This lets Germany land their planes with their stack which prevents Russia from strafing the stack.
Also, I agree 100% with WildBill. If Germany can sucker Russia into attacking with the Leningrad stack they will miss the opportunity to reach the capital in time to help defend. Mostly depends on the size of the stack left behind. Sometimes its meaningless and other times it can cost the game but its definitely not helping Russia protect their capitol.
Also if your playing Germany… The turn before you attack Moscow, try to let Russia take back Archangel if they don’t have it and move the sub out of sz 125. This will give Russia their NO back so you can collect on it when you take Moscow 🙂