Arsene Wenger is desperate to land defensive reinforcements after injuries to Per Mertesacker and Gabriel.
He was forced to bring Laurent Koscielny back early and last week had to pair inexperienced duo Rob Holding and Calum Chambers together.
They’ve taken one point from their opening two games and the fans have voiced their opinions from the stands.
Valencia defender Mustafi is Wenger’s No.1 target but now the Spanish club want Arsenal to pay in full.
Arsenal had been quoted around £25m previously but were trying to bring the price down - and now Valencia are ready to hold out for the whole release clause fee of close to £50m, according to the Daily Mirror.
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Arsene Wenger has been quoted nearly £50m for Shkodran Mustafi
Mourinho has already splashed £30m on Eric Bailly - signing the 22-year-old from Villarreal.
Bailly has impressed for United against Bournemouth and Southampton but Mourinho appears to want even more defensive options.
He has been linked with a move for Jose Fonte at Southampton, but Spanish website Don Balon claims Mourinho really wants Real Madrid ace Varane.
Raphael Varane - 5 things you need to know
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The France defender was given a chance at the Bernabeu under Mourinho but has since seen his playing time limited.
He is behind Pepe and Sergio Ramos in the pecking order under current boss Zinedine Zidane.
However the report does suggest a deal could be difficult to fund following United’s world record signing of Paul Pogba.
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Jose Mourinho is ready to go back into the market
Klopp not at panic station…
Jurgen Klopp says he refuses to panic with the transfer window coming to a close.
But Klopp insists he will not go mad in the final week of the window.
"If one game should change my mind then I would be a real idiot," he said. "I know you would all buy a left-back but a midfielder?
"Emre Can was on the bench, he had a back problem, Lucas Leiva is injured and you ask me for a hard midfield player. The answer is I don't know - we will see."