On Friday, Jon Paul Morosi of MLB.com reported Bumgarner is joined by the Seattle Mariners' James Paxton as well as the Arizona Diamondbacks' Zack Greinke and Robbie Ray among the top starters on the trade block during the offseason.
The 29-year-old lefty has established himself as one of the top pitchers in the National League over the past decade. His resume includes four All-Star Game selections, three World Series titles and a World Series MVP Award from the team's 2014 triumph over the Kansas City Royals.
He's posted a 3.03 ERA and 1.11 WHIP with 1,591 strikeouts in 1,638.1 innings across 255 career appearances (252 starts), all with the Giants. His numbers were slightly elevated in 2018, including a 3.26 ERA, but he didn't show any signs of a significant drop-off.
Injuries have been a bigger concern than performance over the past couple years.
Bumgarner was limited to 17 starts in 2017, his lowest total since becoming a stalwart member of the Giants' rotation in 2010, and he made just 21 starts this past season after missing the first two months because of a fractured finger suffered during spring training.
His contract could also be a hurdle in trade talks. He's scheduled to become an unrestricted free agent after the 2019 season with the conclusion of his five-year, $35 million contract.
Whether a team would be willing to trade San Francisco the type of high-end assets it would likely seek for a pitcher of Bumgarner's caliber in exchange for a one-year rental is unclear.
Ultimately, given the left-hander's contract situation and the relative strength of the pitching market, both via trade and free agency, the Giants may struggle to find a fair-market offer during the offseason.
Waiting until next season's trade deadline, when Bumgarner could be a prized commodity for a contender in need of pitcher, could be the better play if no progress is made on a contract extension.