Japanese left-hander Shota Imanaga's posting period expires on Thursday at 5 p.m. ET, so if he plans to make the move to Major League Baseball, he needs to sign with a team prior to that deadline. The San Francisco Giants, Boston Red Sox, Chicago Cubs and Los Angeles Angels have been tabbed by sources as the finalists for Imanaga, but according to one source, San Francisco might be emerging as the favorite, according to Mark Feinsand of MLB .com.

The Giants have been active this offseason, signing outfielder Jung Hoo Lee to a six-year, $113 million contract and trading for former AL Cy Young winner Robbie Ray, but adding Imanaga would beef up a rotation that will be without Alex Cobb (hip) until June and Ray (Tommy John surgery) until at least July.

Imanaga is expected to command a contract that is worth more than the five-year, $75 million deal that Kodai Senga signed with the Mets last offseason. While the Giants might be emerging as the favorites for Imanaga, the Angels – who also desperately need starting pitching – shouldn't be ruled out.

The Angels signed Zach Plesac last week, but the rotation is still thin. The Red Sox are another club that could still make a move for Imanaga, who would become Boston’s lone left-handed starter following the recent trade of Chris Sale to the Braves.

Imanaga is 64-50 with a 3.18 ERA in 165 games during his career in Nippon Professional Baseball. He had a 2.66 ERA in 24 starts last season, with 188 strikeouts in just 159 innings. The left-handed pitcher also helped Team Japan to the World Baseball Classic title last spring.