Mass with nipple leaking

I brought my 6 year old rabbit (flemish giant) inside this frigid cold evening to keep warm. As I lifted her out of her cage I felt a hard lump under her abdomen. Upon further inspection, she has one nipple by the mass that is leaking clear fluid. The nipple appears healthy--no discoloration, swelling, or heat. When I squeeze the nipple, fluid sprays out. The fluid is clear with a little white tint. She is in no discomfort as I palpate the mass or squeeze the nipple. The mass is hard, irregular in shape, size approx 2"x1"and feels as if it right below the skin. The skin and hair are healthy in this area and she is in no pain. Her activity is normal, eating well, and peeing/pooping well. She is not pregnant. No males. Her last litter was over two years ago. Thoughts or any experience with this? Thank you for your ideas!

any mass is suspect. leaking masses.. to me even more suspect. If she's important to you I'd be taking her to the vet.

Clearly, it's an abscess. I would see a vet immediatly to check it doesn't need an operation. You'll probably need to give her antibiotics at the very least...

Bunny had a pea sized tumor under one breast. She was maybe 10 years old. Had it removed. Never bothered to find out if it was cancerous.