AS says Vietto has pulled out of talks with Sporting CP and is now in advanced negotiations with Los Che. A deal could be settled in the next 24 hours.
The Argentine's agent Sergio Mandrini has already settled on personal terms with Valencia.
Vietto is expected to sign for Atletico on-loan to the end of this season, with the option to move permanently for €15m.
He is traveling to Valencia on Wednesday for a medical as the two clubs put the final touches on the deal.