The move is a tip of the cap of sorts to the 36-year-old who is a free agent after this season.
Lopez (2-2) currently has a 1.99 ERA with 29 strikeouts against 11 walks in 55 appearances and would be a welcomed addition to any bullpen.
As baseball's best lefty specialist, he's remarkably allowed only one home run in 578 batters since coming to San Francisco via trade in 2010.
Though often only facing one batter, he's been used by manager Bruce Bochy as a key weapon to neutralize the games best lefties at the plate in turn helping the Giants win World Series championships in '10 and '12. He won his first ring with the Red Sox in 2007.
The veteran was the subject of interest leading up to last month's non-waiver trade deadline, and any team claiming him would likely have to give up a prospect for his services.