Depends on the reason for setting a certain amount as a minimum.
Tell him that if he doesn't want to accept specific amount as a counter, you will send it to the auction at the minimum pricing that he bid on.
It's really up to you.
Nonetheless, you should talk to him.
I was bidding minimum (mid xxx) on afternic domain, but the seller didn't even bother to reply or counter. I would've went up to mid x,xxx, but I would never bid on his names again.