But earlier, boss Wolff said Alonso might not be a good fit for Mercedes, given the explosiveness of his character and his earlier relationship with Lewis Hamilton.
But Wolff now tells the Spanish newspapers Marca and El Mundo Deportivo: "You cannot say 'no' in advance -- that would be stupid.
"What you can say is that if he is not the best, he is one of the best out there. His energy and motivation are still there.
"He's in the final stages of his career, but that does not mean he cannot win races and titles in the next two or three years," Wolff added.
But as McLaren's former works engine partner, Mercedes was notably burned by Alonso's famously fiery character in the past.
Wolff said: "If you could choose the Fernando today as he is, as a person, it would be much easier than to choose him with all the historical context.
"Lewis plays a key role in this. I think a driver always accepts a challenge, and Fernando would be a challenge.
"But it's much more than just Lewis feeling right with Fernando. The whole dynamic of the team is important. Everything has to fit, but I think Fernando is a different person to how he was in the past," Wolff added.
However, Wolff also said he is happy with Mercedes' current driver lineup, even though Valtteri Bottas is only under contract for a single year.
"The real situation is that, with respect to Alonso, there are other drivers who are a priority -- Valtteri and Lewis first of all.
"We are also excited by our young talents and there are others who please me too. Fernando is part of this group but not more. I fully trust Valtteri, but there are many possibilities for 2018.
"Then there will be a big change in 2019 when all the great drivers will be available," he added.