A man cleaning out an attic in Defiance, Ohio has stumbled on to what some are calling the most important discovery in sports collecting history.  In a dusty, old box, he found what could be a multi-million dollar collection of baseball cards.

Matt Bruning with FOX News Radio affiliate WTVN has more from Columbus, Ohio:

Ty Cobb, Honus Wagner and Cy Young baseball cards - in mint condition - among the 700 cards discovered in a cardboard box, tucked under an old dollhouse. 

(Kissner) "We didn't know what we had.  We just kind of looked at it and went, 'Okay, they're neat.  They're either worth something or they're worth nothing.'  And we put the box lid back on, and went back to cleaning out the attic.

Karl Kissner says his grandfather gave them away as a promotion for his business, and these were likely the leftovers.

(Kissner) "We have a Honus Wager, PSA 10, which is a mint gem.  It is the only one in existence."

The collection could be worth up to $3 million.  

The best cards will be sold at auction in August.

In Columbus, Ohio, Matt Bruning for FOX News Radio.