Rafael Nadal, 32, won five titles in 2018 including his 11th French Open crown.
Whitaker labelled the achievement, in terms of individual Grand Slam wins, ‘greater than anything we’ve ever seen’.
That includes any of the 20 Grand Slams that Roger Federer has won in his glittering careeer.
But Nadal, who struggled with injuries throughout the year, hasn’t done enough to win the tennis expert’s vote for player of the year.
“Apparently, the stats say Rafa’s win percentage for the year is the best, but if we were just referring to stats all evening it wouldn’t be particularly entertaining,” she said on the Tennis Podcast at their annual awards evening.
“His win percentage for the year is best, he obviously missed a lot of significant events for the year so that’s a mitiigation to that.
“To be honest, I do think there’s a case to be made for the fact we all have a bit of Rafael Nadal fatigue because he’s won so many of these clay-court titles.
“He keeps winning these things. Yeah, alright, we thought he’d win the French Open again and he won it again.
“He’s won 11 of them. In terms of achievements at individual Grand Slams, it’s greater than anything we’ve ever seen.
“But I’m not going to pick Rafael Nadal.”
Instead, Whitaker handed her vote to two-time Grand Slam winner Novak Djokovic.
“I’m going to pick Novak Djokovic – it is the biggest rise from where he came from to finish the year as world No.1,” she added.
“That big a leap has never happened in the space of a year before.”