That's because, according to The Daily Mail, Jackson has officially informed the Chelsea hierarchy that he wishes to explore a transfer away from the west London outfit. Chelsea are open to letting Jackson leave and are believed to be talking to suitors about the prospect of getting a deal wrapped up as soon as possible.

The outlet are also reporting that Jackson trained on his own at Chelsea's base in the build-up to the friendly fixture against Leverkusen. Despite this, it isn't believed to have soured Jackson and Maresca's relationship, with suggestions the Senegal international will be welcomed back into the fold, should he fail to secure a move elsewhere.

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Maresca was quizzed on Jackson's situation ahead of the exhibition match, hinting that an exit for the ex-Villarreal ace could be on the cards. He said: "When the transfer window is open, unfortunately or fortunately, anything can happen. This also involves Nico's situation. At the moment we also had two strikers arrive, Joao [Pedro] and Liam [Delap]. So we will see what happens."

Chelsea have spent big this summer in the attacking department, with Pedro and Delap expected to be two of several new forward additions. Jamie Gittens arrived from Borussia Dortmund earlier in the window, while a deal for Xavi Simmons is expected to be completed ahead of the new campaign.

What's more, Chelsea have accelerated talks for Alejandro Garnacho in recent days, with the Manchester United forward believed to be keen on a move to the club. United are said to want rid after a rumoured falling out between Garnacho and Ruben Amorim, with an asking price of £40million having been floated.

Chelsea have until September 1 to complete any deals, with their first game of the new campaign coming at home to Crystal Palace next weekend. They face a relatively comfortable start to the season, with matches against West Ham, Fulham and Brentford making up their first four league matches.