The market for Sporting KC and US youth national team rising star Gianluca Busio continues to heat up.

There has long been interest in the homegrown midfielder and it is reaching a boiling point this summer. SKC rejected offers from two Serie A clubs this winter, as first reported in April by MLSsoccer.com, then received another two from Serie A this summer, as reported by ESPN's Taylor Twellman and confirmed by MLSsoccer.com a few weeks ago.

A source told MLSsoccer.com Friday that Portuguese club Sporting Lisbon as well as a French and Belgian club have joined the ever-expanding list of European clubs interested in acquiring Busio. It is expected more offers from Italy and elsewhere will arrive this summer.

Both Busio and head coach/sporting director spoke of the swirling interest in a wonderful deep dive by KC Star journalist Sam McDowell.

“I’m not forcing my way out. It’s not like that,” Busio told McDowell of the KC Star. “It’s mutual that we both talked about this from the beginning. This has always been the stepping stone.”

What's the market?

As first reported by McDowell, a source confirmed the expectation that Sporting KC will seek at least $5 million plus add-ons and a sell-on percentage for Busio. Those figures would run congruent with recent market movements around MLS.

Last fall, it was Philadelphia Union rising star Brenden Aaronson in the spotlight as a host of European clubs circled. The Union eventually agreed a deal with RB Salzburg, for $6.5 million upfront, with incentives to take the deal to $9 million, as well as a sizable sell-on percentage. A source described those add-ons as "likely" to be met and the sell-on clause to be tiered based on the fee of Aaronson's next transfer.

The deal was agreed before the European transfer window closed, but was set for January 1 so Philadelphia could remain full-strength to finish the MLS season as they chased silverware. They won the Supporters' Shield, with Aaronson an integral driving force. Philly made it clear at the beginning of any transfer talks that they would only agree a deal that kept Aaronson in MLS for the rest of 2020. It's unclear if SKC will negotiate hard for something similar, or if the interested clubs would acquiesce to such an agreement.

Aaronson's transfer could prove as a baseline for Busio, as the parallels between the two are strong.

Busio just turned 19 at the end of May. Aaronson's final year in MLS was his age-19 season, turning 20 just before Decision Day. The pair have a similar number of minutes in MLS and a similar number of goal contributions. Aaronson had seven goals and nine assists in 3,635 minutes while Busio currently has seven goals and six assists in 3,143 minutes. The attack-minded midfielders have also displayed the ability to play multiple positions at a high-level.

Aaronson has broken into the senior US national team over the last year, while Busio on Friday was named to the USMNT's preliminary roster for the Gold Cup later this summer.

Busio has started all nine of SKC's games this year, with two goals and an assist as he's played as a false nine, attacking midfielder, box-to-box midfielder and a defensive midfield role. The club sit second in the Supporters' Shield race, with about a quarter of the season gone.