Dimitar Berbatov says Gareth Bale "is too gifted to sit on the bench" and that "something is not right" with the Real Madrid outcast at the Bernabeu.
Bale hasn't seen a single minute of action since returning from lockdown, having been an unused substitute in eight of Madrid's final 10 La Liga fixtures.
The 31-year-old was also a surprise omission from Zidane's 22-man squad for last week's Champions League quarter-final second-leg tie against Manchester City, which the Blancos lost 2-1 at the Etihad Stadium.
Ahead of that clash, the Frenchman explained that Bale had asked to be left out, but also insisted that he still enjoys "a relationship of respect" with the experienced winger.
Despite Zidane's comments, rumours of a rift in the dressing room have persisted, and Madrid are being tipped to cash in on the Wales international during the summer transfer window.
Berbatov has admitted to being perplexed by Bale's current situation, having seen him win four Champions League crowns and two La Liga titles since moving to Santiago Bernabeu from Spurs in 2013.
The Bulgarian, who also enjoyed a spell at Tottenham at the height of his career, wants to see the Welshman back on the pitch as soon as possible, with his considerable talents going to waste while he remains on the sidelines.
"When I heard that Gareth Bale didn't want to play, I was surprised and even more surprised that Zidane revealed it to the media," Berbatov told Betfair.
"Something is not right over there with him. If he's fit, it is awful that he doesn't play. When a player refuses to do that, it confuses me a lot.
"Gareth, I want to see you play football! He is too gifted to sit on the bench."
The ex-Spurs star did, however, go on to to defend Zidane in the wake of Madrid's Champions League exit, with a 4-2 aggregate loss to City in the round of 16 considered nothing more than a "blip".
Berbatov added: "People are so fickle. Zidane has won the Champions League three times in a row, Real had never been eliminated under him until their defeat to Manchester City.
"Now all of a sudden one blip and people are going crazy. People will build you up just to crash you back down again and it's very wrong.
"It's not the end of the world that they got knocked out of the Champions League in this crazy year. City are a very strong team, if you make mistakes you will get punished against them, that's life."