Alex Rodriguez is putting his time on the NY Yankees disabled list to good use ... by jumping in the real estate game and unloading his GIANT Miami mansion for a whopping $38,000,000. Cha-ching!

A-Rod bought the super modern crib back in 2010 -- while it was still under construction -- for a reported $24 mil. But now he's looking to sell off the 20,000-square-foot pad and make a cool profit at the same time.

The 9-bedroom, 11-bath beachfront estate is freaking AMAZING if you've got the cash. It offers 275 ft. of water frontage, a home theater, a heated pool, gym, rooftop deck, an elevator AND a 3,000 square-foot sports room complete with a batting cage.

Hey, even McKayla Maroney would be impressed.