The Cardinals and Rockies have begun exchanging names in their discussions about a blockbuster trade involving superstar Nolan Arenado, one source told MLB.com on Tuesday.

While it¡¯s too early to tell if there is momentum toward a deal, the source said negotiations have advanced beyond a preliminary stage.

In order to move Arenado, the Rockies are insisting on a package that includes a combination of Major League talent and at least one prospect.

Colorado has interest in St. Louis right-hander Dakota Hudson, who went 16-7 with a 3.35 ERA in 33 games (32 starts) last year, but Rockies officials are wary of Hudson¡¯s MLB-high walk total. There is no indication that the Cardinals are willing to include star right-hander Jack Flaherty in a proposal for Arenado.

The Rockies also are expected to ask for at least one of the Cardinals¡¯ top four prospects, as ranked by MLB Pipeline: outfielder Dylan Carlson, third baseman Nolan Gorman, left-hander Matthew Liberatore (acquired from the Rays last week) or catcher Andrew Knizner.

While St. Louis veteran Matt Carpenter is one candidate to be included in the deal -- based on his ability to play either infield corner in Colorado -- the Rockies don¡¯t appear to be mandating his inclusion.

Arenado is owed $234 million over the next seven years, and a separate source said the Cardinals are concerned about the opt-out he has following the 2021 season. The Cardinals likely would ask Arenado to waive the opt-out clause as a condition of the trade, possibly in exchange for adding more guaranteed money to the contract.

Arenado has a full no-trade clause but is said to be intrigued by the opportunity to play for a team with the most World Series titles of any National League franchise. Arenado¡¯s strong relationship with St. Louis first baseman Paul Goldschmidt -- with whom he won a gold medal for Team USA at the 2017 World Baseball Classic -- contributes to Arenado¡¯s openness to approving a deal to the Cardinals.

Derrick Goold of the St. Louis Post-Dispatch reported that the Cardinals have had interest in trading for Arenado for more than a year. Arenado, 28, has won seven NL Gold Glove Awards at third base and been selected to five All-Star teams. Industry sources consider him more likely to be dealt in the coming weeks than fellow stars Mookie Betts and Francisco Lindor.