Mares (24-0-1, 13 KO) last fought on April 21, when he rather routinely routed veteran Eric Morel in a one-sided but entertaining enough Showtime main event. The 26-year-old Mexican has been showcased by the network as he's made a name for himself at both 118 and 122 pounds, and has become a go-to guy for Showtime in the last couple of years.
With this slot, he wouldn't be expected to face a top fighter, but probably something more in line with the Morel fight, which was a stay-busy, non-challenge, no matter what anyone at Golden Boy might have tried to sell you. There are plenty of quality fighters at 122 (or at 118 to come up) who could make for an entertaining TV bout with Mares on September 15.
Also on the undercard will be a WBC featherweight title scrap between Jhonnny Gonzalez and Daniel Ponce De Leon. Canelo vs Lopez will air live on Showtime, going head-to-head with the Chavez Jr vs Martinez pay-per-view from HBO.