Bale, 27, has not played since limping off after 39 minutes of a 3-2 defeat to Barcelona on 23 April having suffered the recurrence of a calf injury that previously left him sidelined for several weeks.
The former Tottenham Hotspur forward appeared to be making a steady recovery, however, featuring in Zinedine Zidane's squad on the final day of Real's league campaign and returning to full first-team training five days ago along with Dani Carvajal, who has been recovering from a hamstring injury.
Speaking at a press conference on Tuesday, Zidane remained coy on his selection plans amid calls for Isco to start ahead of the Welshman, whatever condition he finds himself in on match day. But the Real Madrid boss appeared to have no concerns over Bale's fitness.
"Gareth does not have to say anything to me. He is ready. He is with us. He has a tremendous motivation because he plays at home. I'm only interested in that," he said.
But Bale now admits Saturday's final against the Bianconeri may come too soon for him, concerned that an ankle ligament injury suffered in November which required surgery is now hampering his hopes of starting in Cardiff.
"I am not 100%: I haven't played for six or seven weeks: I obviously had my operation which still really hasn't recovered," Bale said, The Guardian report. "If I'm called upon to start, I will start obviously. But to last 90 minutes: I haven't played a lot of football this year since my operation, so that would be difficult.
"Isco has been playing fantastically well for us, at the end of the season, so whatever the manager decides I will [accept it]. Whether he or I start, we'll both be cheering each other on."