The Argentine basically has no future at City after first refusing to warm up in a Champions League game in late September and then had a further fall-out with club officials when he did not report to training and traveled back to his homeland.
Riso, who is serving as a liaison between Tevez's representative Kia Joorabchian and AC, is confident that some sort of contract will be signed but has revealed that there are some difficulties to be ironed out.
"One thing is certain, the player wants AC Milan and there is a strong desire by the Rossoneri to negotiate [a deal]," he told Goal.com.
"The negotiation is a difficult one and there are many obstacles. We are still at the beginning and it is too early to say whether the deal can be done or not.
"In the first meeting, there was no talk of figures. They are only the basis for continuing the discussion between the parties. Now we will try to discover if the operation is feasible or not, also in economic terms."