Froome maintains the red leader's jersey after losing 42 seconds to Nibali and 1-16 minutes to Alberto Contador (Trek-Segafredo). Stefan Denifl (Aqua Blue Sport) won the stage from an escape.
"Absolutely not!" Nibali said when asked if Froome showed any weakness in stage 17.
"Up until the last climb, he had seven men. It's the same solid Team Sky."
Froome rode in the slipstream of Sky team-mates Wout Poels, Gianni Moscon, Mikel Nieve and Diego Rosa on the last climb. Nieve paced him the last kilometres after Contador attacked.
Contador rode free, but could not catch the lone Austrian Denifl. Behind, Froome seemed unable or unwilling to follow the other classification rivals.
A group with Nibali and Wilco Kelderman (Sunweb), second and third overall, moved free. Nibali finished 42 seconds ahead of Froome and moved from 1-58 to 1-16 minutes back, cancelling out most of the gains Froome took in the time trial yesterday.
Three-time Vuelta a España winner Contador came within 28 seconds of Denifl. A stage win would have capped off his career as this is his final race.
"It's truly a pity that I couldn't win the stage," Contador said. "It was a good stage, but even more so because my legs responded when I attacked.
"When I got out of the saddle, the bike took off. I knew which wheel I had to follow, and that was López. When he jumped, I was a little bit behind, and when I caught up to him, I decided to go alone. I knew that no one would be attacking with as much conviction as I would be."
With the gains, Contador sits 3-34 behind Froome in fifth place. He trails Kelderman, who sits at 2-13, by just over a minute.
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