In October, Greer stirred outrage when she accused Jenner of transitioning in order to outshine her children and step-children who appear on Keeping up With the Kardashians.
The 76-year-old Australian writer said: "He/she wanted the limelight that the other, female, members of the family were enjoying and has conquered it, just like that."
Redmayne, who plays transgender artist Lili Elbe in The Danish Girl, said he disagreed with her provocative comments.
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The 34-year-old London-born actor told British GQ: "I completely disagree with what she has to say about Caitlyn in relation to why she is making her show.
"It's a shame to see an instance of feminism and trans issues diminishing each other. But also, it's quite important that this is a singular instance, and most feminists ally with the transgender. But specifically, I just disagree with her."
Greer, one of the key figures in the second-wave feminist movement, enraged the trans community after claiming that “lopping off you d**k and wearing a dress doesn’t make you a f***king woman”.
Despite her remarks, Redmayne expressed admiration for Greer: "Of course, Germaine Greer is a woman with extraordinary strength and conviction, but I disagree."