The WWE superstar posted the photo on Instagram ahead of McGregor's UFC 257 fight against Dustin Poirier.
The t-shirt is part of McGregor's charity and all of the proceeds from t-shirt sales will go to 'Roots of Fight', which will benefit the Children’s Health Foundation Crumlin that supports Children’s Health in Ireland.
"All of us Irish champs stay ready," Lynch wrote in the caption.
"All profits will benefit the children's health foundation crumlin that supports children’s health In Ireland," she added.
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Earlier, Lynch had posted photos of her pregnancy with fiance Seth Rollins, which had gone viral. She had shared six pictures in a carousel.
She had relinquished the RAW Women's Championship to Asuka after announcing her pregnancy and is expected to be back to challenge for the top again.