When Pablo Sandoval departed for the Boston Red Sox earlier this offseason the Giants knew they had a big vacancy to fill. Well, they still do, after failing to sign a number of free agents who could have taken over at third base for 2015. What's next for San Francisco?

Perhaps their top two free-agent options signed with other MLB clubs on Monday. Third baseman Chase Headley re-signed with the New York Yankees on a four-year, $52 million deal and infielder Jed Lowrie landed with the Houston Astros on a three-year, $23 million contract. This has left the free-agent market thin in terms of infielders, specifically those capable of playing third base.

As a result, Chris Haft of MLB.com says San Francisco might have to begin exploring trade options to find a desirable third baseman. He mentions Cleveland Indians third baseman Lonnie Chisenhall, Miami Marlins third baseman Casey McGehee and Boston Red Sox third baseman Will Middlebrooks as potential targets. We're going to throw in Houston Astros third baseman Matt Dominguez to make things interesting since McGehee is an unlikely option because he just won Comeback Player of the Year and is the Marlins only definitive option at third.

The Red Sox have perhaps been the most active team this offseason after signing a number of free agents and executing a number of trades. With Sandoval in town, there's no need for Middlebrooks, especially since they have solid depth with Brock Holt and Garin Cecchini behind him. Holt and Cecchini could be options for San Francisco as well, but Middlebrooks has the most big league experience and has shown what he's capable of. The 26-year-old has slashed .237/.284/.411/.695 with 34 home runs and 122 home runs in 232 career games.  However, any of these players would be decent acquisitions because they're all young and have time to develop.

Chisenhall, another 26-year-old, has played 345 games in four seasons with the Indians and amassed a stat line of .260/.310/.417/.727 with 36 home runs and 133 RBIs. Although the Indians might not want to trade him because of his solid offensive production, Jeff Ellis of Indians Baseball Insider writes "his walk to strikeout total, defense, and inconsistency are all big issues." Trading Chisenhall came up back in 2013, but Cleveland didn't want to give him up because they believed he was too valuable at the time. That may have changed since the Indians have Mike Aviles and youngster Zach Walters who are capable of playing third. Prospect Francisco Lindor should be called up soon to be the team's full-time shortstop, so maybe the Indians are looking to move around their infield and get value elsewhere.

Dominguez is the final possible option. The 25-year-old played his first two full seasons with the Astros in 2013 and 2014, showing his capabilities as a power hitter. In 340 games with Houston, the former first round pick has slashed .233/.274/.376 with 42 home runs and 150 RBIs. However, his numbers dropped in 2014 after he posted a stat line of .215/.256/.330/.586 with 16 home runs and 57 RBIs in 157 games. The Astros just signed infielder Jed Lowrie, who is expected to play shortstop in 2015, but when prospect Carlos Correa is called up, they might move Lowrie to third. With Lowrie now in the picture, Dominguez could be traded and would likely get value in return since he's under club control through 2018. Although there has been no speculation about such a deal, Evan Drellich of the Houston Chronicle noted Lowrie's arrival "doesn't mean [he] can't or won't play third base at some point." There's a chance Dominguez may no longer be appealing to the Sabermetric-focused front office of the Astros.

The Giants need to get on this roster hole quick because they can't afford to have an inexperienced starting third baseman in 2015.