If Liverpool are only able to make one signing before the transfer window closes on September 2, it should be Paris Saint-Germain defender Mamadou Sakho.
What? The Reds are crying out for a winger or another creative midfielder I hear you say. I would have to disagree.
A top-class centre-back should be top of Brendan Rodgers' wish list.

Why a centre-back?
If Rodgers was mulling over bringing in defensive reinforcements before his side's Capital One Cup win over Notts County, a combination of injuries and lacklustre defending against the struggling League One outfit has probably made his mind up for him.
Liverpool were 2-0 up and cruising when Andre Wisdom and summer signing Kolo Toure's indecisiveness allowed County to peg one back before later equalising and forcing extra time.
Rodgers has already stated that he feels Wisdom would benefit from going out on loan and getting regular game time under his belt, meaning he is more than likely to leave Anfield on a temporary basis in the coming days.
Hi-res-178223090_crop_exact Laurence Griffiths/Getty Images
Toure stretchered off during win over Notts County

While Toure has slotted into Liverpool's back four very well since his switch from Manchester City and looks to have developed a solid understanding with fellow centre-back Daniel Agger, the sight of the big Ivorian being stretchered off with a suspected groin tear during his last outing has left Rodgers fearing the worst.
Toure could face a long spell on the sidelines.
With Martin Skrtel last season struggling for form and fitness, Sebastian Coates ruled out for the season and Agger's own fitness record somewhat questionable, it is vital that Rodgers adds to his back line before the window slams shut.
Martin Kelly is another option but has failed to even make the bench so far this season, and although I personally feel Kelly could be a big asset for Liverpool this season, it appears Rodgers may need convincing.

Why not an attack-minded flair-player?
While the Reds continue to be linked with a host attacking players such as Christian Eriksen, Victor Moses and Arda Turan, with reports from the Daily Star, Daily Mail and Daily Mirror respectively, their quality going forward has been evident during their opening two Premier League fixtures, despite only recording two 1-0 wins.
The opening-day win over Stoke City saw the Reds hit the woodwork on more than one occasion, and the fact that visiting goalkeeper Asmir Begovic was named man of the match tells its own story.
The likes of Daniel Sturridge, Philippe Coutinho, Iago Aspas and Raheem Sterlng have already shown that they can all be a threat in the final third, and with Luis Suarez still to return following his 10-match ban and the likes of Steven Gerrard and Jordan Henderson always looking to get forward, the Reds appear to be reasonably well stocked in attack.
Although that marquee signing that all Liverpool fans crave would be nice, I can't help but feel the need for defensive cover is far greater, which brings me to Sakho.

Why Sakho?
Sakho has been linked with the Reds on numerous occasions throughout his career, and, despite seeming to have been around forever, the French international is still only 23.
Despite being in his early 20s, Sakho has made well over 100 appearances for Paris Saint-Germain so would bring with him a fair amount of experience, having also appeared 14 times for Les Bleus.
It appears however that he is growing frustrated with life in the French capital and is reported to have expressed a desire to make the move to Merseyside, with Metro stating that he is even willing to lower his wage demands to make the move happen.
It will be refreshing for Reds fans—if true—to see a player show such willingness to join the club, especially after the farce that was the will he, won't he Willian transfer saga.
He also been known at times to operate at left-back, which, following the recent injury to another new signing Aly Cissokho, means if needed Sakho could provide cover for the Reds only recognised fit left-back Jose Enrique.
Despite club president Nasser Al-Khelaifi describing Sakho as "a child of PSG, just like Steven Gerrard is at Liverpool" to l'Equipe (via The Mirror) a fee of around £8m has been mooted by Metro as the figure it would take to convince the PSG hierarchy to part with the gifted defender.
Hi-res-161922360_crop_exact Harold Cunningham/Getty Images
Sakho won 76.4% of his aerial duals last season

During the 2012/13 season, he boasted a 76.4 percent aerial success rate during the Ligue 1 campaign, significantly higher than his would be rivals, Toure (40 percent), Agger (61.2 percent) and Skrtel (69.9 percent) while only PSG teammate Thiago Silva (6.3) averaged more than Sakho's six clearances per game throughout the campaign according to WhoScored (via talkSPORT).
At just 23 years of age, Sakho appears to represent good value for money at just £10m, but with reported interested from AC Milan according to The Mirror, the Reds will have to act quickly if they are to avoid missing out on another of their top targets.