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Gallagher had flown to Spain last week to finalise the move, but the transfer stalled after the collapse of an agreement over Samu Omorodion going the other way.

The England international, who has made 95 appearances for Chelsea in all competitions, netting 10 goals and registering 10 assists, has since returned to London while negotiations continue.

Maresca confirmed that while Gallagher has returned, he is training separately while talks between the clubs are still ongoing.

"Gallagher is back and he is training. He is doing some medical tests and training separately, so he won't be involved in this game," Maresca said.

"He is also trying to find a solution with the club, so we will see what happens.

"Unfortunately, these things happen every summer. All clubs have problems but, hopefully for him, this situation will finish where the player, club and manager will be happy."

Chelsea has already bought nine additions in the transfer window, meaning Maresca has 43 players to work with in his squad, and reports suggest more could be coming, with Joao Felix and Victor Osimhen being linked to the Blues.

Having stepped in to replace Mauricio Pochettino, who only spent one year with the club before departing, the Italian has asked for patience as he tries to find the right balance.

"Some clubs work with a manager for eight years, so with time we will close the gap and hopefully that can happen soon," Maresca added.

"Sometimes it sounds like an excuse from managers, and I know timing in football is difficult, but in our case, with the process and ideas, we will close the gap.

"We need their [fans'] support because when you are on the pitch, and you can hear the fans behind the team, it is like 12 players. If they support us and be patient, then we will pay them back with performance and results."