Dortmund want to prepare for the new Bundesliga season without distraction, and according to BBC Sport that means the club have made August 10 their final day to talk transfers.
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The Bundesliga does not start until September 18, while the transfer window closes on October 5.

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However, the report means United could have just one more week to finalise a deal for Sancho, who has long been linked with a move to Old Trafford.
Dortmund want around £100m for the England forward, but United are said to be holding out to drive the price down, while they are set to pay any amount in instalments.
According to Fabrizio Romano, talks are at an advanced stage between United and Dortmund, with personal terms not deemed to be a problem.
Sancho is set to sign a five-year deal at United should the two clubs agree a fee, while Dortmund want enough time to seek a replacement.
United’s desire to pay in instalments is similar to the deal which brought Bruno Fernandes over from Sporting in January.
Fernandes cost United an initial 55m euros (£47m), with add-ons potentially taking the overall fee to 80m euros.

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Our view: United struck gold with Fernandes, while the deal was one of Ed Woodward's finer moments regarding recruitment.
In this instance, clearly it could take a while before Dortmund and United come to some sort of agreement, as the latter will not want to go too high with an offer the German's will readily accept.
As ever with moves of this magnitude, it's a long, drawn out process, but the reported deadline adds a new twist to the saga. Do Dortmund really want to speed up this sale? And will United abide?
United will want to pay the right amount, but signing Sancho sooner rather than later is no bad thing, particularly with rivals Chelsea getting a good look at their new recruits already.
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