The one player Chelsea must sign before the opening day of the season

The start of the Premier League season is less than one month away - who do Chelsea need to sign before the campaign kicks off?

Chelsea's first season back under Jose Mourinho's management ended without a trophy, as the Blues slipped away from top spot and lost to Atletico Madrid in the semi-finals of the Champions League. Next season is expected to be better and ultimately more successful, particularly after the spending the club has already sanctioned this summer.

Barcelona midfielder Cesc Fabregas and Atletico Madrid duo Filipe Luis and Diego Costa have arrived at Stamford Bridge for a combined fee of around £80m, and the club can also count upon returning loanees Thibaut Courtois, Kurt Zouma and Romelu Lukaku next season.

However, there could still be more arrivals this summer. Another central defender and central midfielder could be on Mourinho's transfer wishlist, but adding more striking firepower must be at the top of the list - despite the arrival of Spanish international Costa. Demba Ba has signed for Besiktas and Samuel Eto'o was released upon the expiration of his contract, leaving Fernando Torres as the only other recognised striker behind Costa.

At least one other centre forward should be brought in, and there appears to be no doubt as to who Mourinho wants to sign - Didier Drogba. The former Blues legend is a free agent having left Galatasaray, and speculation continues to suggest that Chelsea will be signing Drogba on a one-year deal, where the Ivorian would also join Mourinho's coaching staff.

At 36, Drogba doesn't have a lot left in the tank, but he showed at the World Cup how his physical presence can unnerve defences, and that's certainly what he'd bring off the bench for Chelsea. Spending big money on a player who would clearly be second choice to Costa would be foolish at this stage, so it makes sense to give Drogba another year at Stamford Bridge before assessing youngster Patrick Bamford's development in 2015.

Drogba's return is what most Chelsea fans are praying for, given his heroic status at the club - and whilst his best days are clearly behind him, he would definitely still play a role for the Blues next season if they sign him.

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