To take Penn's place, Florida recalled right-hander Tim Wood from Triple-A New Orleans.
Penn was 1-0 with a 7.77 ERA in 16 games this season. He allowed four runs -- one earned -- and walked four while getting just one out in a 9-6 loss to Milwaukee on Wednesday night.
This is Wood's first big league stint. He was 1-0 with a 0.54 ERA in 14 games with New Orleans.
Florida has 10 days to trade, release or send Penn outright to the minors.
Also, right-hander Rick VandenHurk was reinstated from the 60-day disabled list and optioned to New Orleans.
To make room on the 40-man roster for VandenHurk, right-hander Carlos Martinez was outrighted to New Orleans.