Check out my post further down the health issues page entitled 'blood blister'. Blues turned out to just be an old small scar he keeps bumping or rubbing. It kept coming and going for a couple of months now it is all cleared up. Like you I was thinking the worst as it was close to his man nipples. If you are worried get him to the vets but it sounds just like Blue.

Ax

Both our two have had blood blisters. They can be absolutely massive - Pearly once had a couple of her shoulder and they were each the size of eggs! Most alarming, but they didn't bother her in the least. We took her to the vet who drained the fluid but they came up again.

Harry once had one on his face, after he charged into me in the garden whilst doing his usual mad moment of running round like a daftie. Unfortunately, he scratched at it and it burst! The kitchen looked like a bloodbath! He ended up wearing one of those lampshades for 2 whole weeks till it healed. Good job he's such a patient lad. Anyhoo, he was none the worse for wear because of it - and it didn't spoil his looks, cos he's still as handsome as ever!