Liverpool's dire need for a centre-back laid bare in FA Cup defeat

Liverpool just cannot catch a break at the moment.

Going into their FA Cup tie against Manchester United, the focus was on their lack of prowess in front of goal - and with good reason. Take out their unconvincing 4-1 win over Aston Villa's kids and they had only scored once in their previous five games, with the Reds drawing a blank in each of their last four.

Once considered the best forward line on the planet, Sadio Mane, Mo Salah and Roberto Firmino's superhuman powers were being seriously questioned for the first time in years.

Jurgen Klopp would have watched on in relief on Sunday, then, when Firmino and Salah combined brilliantly to give their side the lead at Old Trafford. The strike was classic Liverpool; Firmino created space for himself by dropping between the lines, before slipping an inch-perfect through ball into his teammates' path. Salah then finished in typically clinical fashion, lofting the ball cheekily over Dean Henderson.

It would not be the last time the pair would combine, either. Liverpool's second goal was even more Klopp-esque, with his side turning defence into attack within seconds. It started when Edinson Cavani's hopeful pass was picked off by a ferocious James Milner. He then played a clever one-two with Firmino - whose tendency to float had once again left him in acres of space - before shifting it on for Salah to smash home.

Recent form would suggest that these two strikes would be enough for Liverpool to secure the win. That bizarre 7-2 drubbing at the hands of Villa aside, the Reds have only conceded 15 times in 18 Premier League games this season. That is despite the absences of starting centre-backs Virgil van Dijk and Joe Gomez.

However, as has been typical of Liverpool's whack-a-mole season, just as one problem seemed to be solved, another reared its ugly head. Namely, Rhys Williams' complete lack of suitability for the top level. Against United, the 19-year-old looked worryingly out of his depth. An early misstep set the tone for his unconvincing performance, with the nadir coming in the buildup to Marcus Rashford's goal, which made it 2-1 to United.

Failing to make a routine clearance allowed Rashford a clear run at goal and the country's de facto Leader of the Opposition made no mistake, calmly slotting home. This is not Williams' first high-profile blunder either. Against Villa in the previous round, 17-year-old Louie Barry left him for dead to open the scoring, and he also struggled after coming off the bench during his side's 1-1 draw with West Brom last month.

Of course, none of these errors are the youngsters' fault and let us not forget his performance wasn't all bad - he did win a game-high five aerial duels after all. Instead, the culpability lies at the door of his club, who remain fanatically opposed to the idea of recruiting a defender in January.

For context, this time last year, Williams was coming to the end of his loan spell with Kidderminster Harriers in the sixth tier of English football.

To expect him to suddenly be ready for the top level is not only unreasonable but entirely irresponsible from the Reds, with such knocks to Williams' confidence at such an early stage in his development on such a big stage potentially detrimental to his future.

Fine margins are often what decide games like the one against United on Sunday. The fact of the matter is that with a proven centre-back partnering Fabinho, Liverpool would have taken the game to extra time.

There is still time for the Reds to rectify the situation, but they need to move fast in order to fix a problem that has been clear to everyone else for some time.