The Chicago Cubs already spent $155 million on Jon Lester earlier this offseason, but they might not be done upgrading their starting rotation. Sources say the team is interested in another notable free-agent pitcher.

According to David Kaplan of CSN Chicago, the Cubs are "kicking the tires" on James Shields and they are one of the teams the free agent is considering as he mulls his contract offers. The 33-year-old is expected to make a decision by the end of the week, and it's believed more teams have gotten involved because his price tag has dropped.

Initially, Shields was seeking a five-year contract in excess of $100 million, but due to a number of concerns regarding his age, durability and ability to keep pitching at a high level (he has thrown at least 200 innings in each of the past eight seasons), it has been said his value has decreased to a deal in the four-year, $70 million to $80 million range. Chicago is currently sitting at a $112 million payroll for the 2015 season, so they have some room to work with if they were to add Shields.

What's also interesting is Kaplan reported on Wednesday night that he expects the Cubs to "have a deal done for [catcher] Wellington Castillo and possibly [starting pitcher] Travis Wood" before the team head s to spring training in Arizona. They currently have eight starters on their depth chart and Wood is listed as the No. 5 spot in the rotation, which could be an indication they like their chances with Shields.

Let's not forget the right-hander started his career back in 2006 with the Tampa Bay Devil Rays, which is also when Joe Maddon was hired as the team's manager. The two spent seven seasons together before Shields was traded to the Kansas City Royals prior to the 2013 season.

Phil Rogers of Sports on Earth makes a good point on how and why the Cubs can make this happen:

"The lineup then will be loaded with kids like Kris Bryant, Jorge Soler, Addison Russell, Javy Baez, Albert Almora and Kyle Schwarber, most of whom would be just starting their arbitration years. And if Russell does make Starlin Castro expendable, that will save about $10 million a year for three or four years."

"All those young hitters put the Cubs in position to spend a disproportionate amount on starting pitching through at least 2018. Those years can be used to develop a group of young starters to work in front of a loaded lineup in 2019 and beyond, when guys like Bryant, Soler, Schwarber and Russell will be in the prime of their careers."

With only $82 million on the books for the 2016 season, it's likely the Cubs also chase one of the top free-agent pitchers during the 2015-2016 offseason.