The Colorado Rockies and St. Louis Cardinals have reportedly advanced past the preliminary stages of trade talks involving All-Star third baseman Nolan Arenado.

According to MLB.com's Jon Paul Morosi, the Rockies and Cardinals "have begun exchanging names," and the Rockies have insisted on a package that includes "a combination of Major League talent and at least one prospect" in return for Arenado:

Arenado is owed $234 million over the next seven years, but he can opt-out after the 2021 season. Morosi added the Cardinals would likely ask Arenado to waive the opt-out clause as a trade condition.

While it is unclear precisely who the Rockies and Cardinals have mentioned, Morosi noted Colorado is interested in Cards starting pitcher Dakota Hudson.

The 25-year-old Hudson went 16-7 with a 3.35 ERA and 136 strikeouts in 174.2 innings pitched. Morosi added the Rockies have some concerns about Hudson's walk rate, though, as he issued a Major League-leading 86 bases on balls last season.

Morosi also reported 24-year-old pitcher Jack Flaherty is not believed to be in play even if the Rockies would likely love to add him to their moribund starting rotation.

Additionally, Morosi has heard that the Rockies are likely to require one of the Cardinals' top four prospects to be included in the deal: outfielder Dylan Carlson, third baseman Nolan Gorman, pitcher Matthew Liberatore or catcher Andrew Knizner.

The Cards acquired Liberatore in a trade with the Tampa Bay Rays last week, and it was immediately speculated he could potentially be flipped to Colorado as part of an Arenado trade due to the Rockies' need for young arms.

Colorado had the second-worst team ERA in Major League Baseball last season at 5.56, so it is safe to assume that the return for Arenado would be pitching-heavy.

Another name mentioned by Arenado as a potential part of the deal is Cardinals veteran corner infielder Matt Carpenter. Since the Cardinals would have Arenado and Paul Goldschmidt at third and first, respectively, they would have no need for Carpenter, and he could be a quality replacement for Arenado in Colorado.

Morosi added that although Carpenter's inclusion would make sense, it hasn't been demanded by the Rockies.

Whatever package the Cardinals assemble, it will likely have to be a talent-laden one in order to pry Arenado away from the Rockies. While trading Arenado would create salary relief, Colorado would also be moving one of the best all-around players in baseball.

The 28-year-old is a five-time All-Star, seven-time Gold Glove winner and four-time Silver Slugger winner who hit .315 with 41 home runs and 118 RBI.

Arenado has posted at least 37 homers and 110 RBI in five straight seasons, and with him and Goldschmidt anchoring the lineup, the Cardinals would arguably be the team to beat in the NL.