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Juventus shares were down 17.7 percent at 1.39 euros at 0730 GMT after plunging nearly 21 percent when trading in Milan began.
Shares in the Turin-based club had risen sharply last year following the signing of Ronaldo from Real Madrid.
A young Ajax team stunned Juventus to reach the Champions League semi-finals for the first time since 1997 as Matthijs de Ligt's second-half header secured a 2-1 second-leg victory in Italy on Tuesday.
The defeat halted Ronaldo's bid for a sixth Champions League title.