Lewis Hamilton and Valtteri Bottas will line up first and second on the grid for Sunday's grand prix, but the long run pace and tyre management of Red Bull driver Verstappen has caused concern for Wolff.
The Dutchman was triumphant in similarly hot temperatures last time out at Silverstone, and although impressed with the improvements made by the Mercedes team, Wolff tagged Verstappen as the favourite.
"I believe the work that has been done during the week and from yesterday to today was good," said Wolff. "I think we have improved and that is most important, and I hope we can give him a run for his money, but definitely Max needs to be seen as the favourite based on yesterdays long runs.”
In response to comments about the similarities to one week ago, Wolff added: “The only similarity between Silverstone and Barcelona this week is the ambient and the track temperatures, but the track itself is very different.
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