United States international Christian Pulisic has an agreement in principle on a long-term deal to leave Chelsea and move to Serie A giants AC Milan; however, the clubs have yet to agree on a transfer fee, a source in Italy with knowledge of the situation told ESPN.

Pulisic, 24, is willing to take a substantial pay cut to make the transfer work, the source added, with only minor details still to be worked out before a full agreement on personal terms can be reached.

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There remain negotiations on the fee, with Chelsea wanting €25 million ($27.3m) while Milan is thinking more in the €15m-€18m range, the source said.

The news was first reported by Italian outlet Tuttomercatoweb.

Chelsea is of the belief that Sandro Tonali's expected move to Newcastle United means Milan can afford to pay more, but Milan want the proceeds from that deal to help them acquire three to four players. This stance is creating some impatience on the Milan side and they are considering walking away from the deal.

Pulisic, however, only wants to go to Milan.

Pulisic, a €64m signing from Borussia Dortmund in 2019, has 12 months remaining on his contract at Chelsea. With the club needing to reduce the size of their squad and wage bill after spending more than £600m ($762m) on new players since a consortium purchased the club a year ago, sources have said Pulisic is high on the list of potential departures.

A number of clubs have been approached about the prospect of signing Pulisic, with sources previously telling ESPN that Manchester United, Newcastle, Napoli, AC Milan and Galatasaray have all been made aware of the player's likely fee and salary, which sees him earn £13m per year at Chelsea.

Pulisic has endured an injury-hit time at Chelsea over the past two seasons. He was booed by a small section of the club's supporters when introduced as a second-half substitute during the final game of last season at home to Newcastle.

With Chelsea adding forwards Mykhailo Mudryk, Raheem Sterling, Noni Madueke, Pierre-Emerick Aubameyang and David Datro Fofana to their squad -- as well as the loan signing of Atletico Madrid's Joao Felix -- in the past year, Pulisic fell out of the picture at the club and had been set to leave on loan in January but for a knee injury that led to him being sidelined for two months.

Information from ESPN senior writer Mark Ogden was used in this report.