Liverpool have suffered disappointing news this week, with central defender Sebastian Coates returning from international duty with a serious knee injury requiring surgery.
The Uruguayan suffered an anterior cruciate ligament tear, as per Mirror Football, while away with his nation preparing to face Japan in the week before the opening Premier League match, and he now faces around six months of rehabilitation and recovery.
While Coates has not been anything like a regular starter in his time at Anfield so far, making just 24 appearances in all competitions in two years, his unavailability means that Brendan Rodgers is likely to have to rethink some transfer plans.
The Reds lost Jamie Carragher to retirement this summer and responded by filling that gap with Kolo Toure on a free transfer, but he remains the only incoming defender so far.
Toure started the first Premier League game of the season alongside new vice-captain Daniel Agger, with young defender Andre Wisdom on the bench. Martin Skrtel is the other senior centre-back in the squad, though he suffered a knock at the end of preseason, with Martin Kelly and Coates himself the other options for manager Rodgers to turn to.
Skrtel in particular
For several seasons, Martin Skrtel has been one of the two centre-backs regularly playing for Liverpool. He has partnered Carragher, he's been alongside Agger and has even played as part of a back three at times.
While he looks fearsome and can certainly throw a few strong challenges around, Skrtel's big problem has been a lack of aggression and a failure to significantly improve his game from being merely a quite good defender to becoming a top one.
Last season's alteration of the Reds' back line to being the starting point for many attacks didn't suit him as he struggled to maintain his level of performance when asked to play both higher up and closer to the right touchline to open up the pitch for playing out of the back. He eventually lost his place in the new year and seemed likely to leave the club this summer.
Coates' injury, however, might change all that.
Andre Wisdom's future, Martin Kelly's recovery
Wisdom spent most of last season filling in at right-back for the Reds but has played out preseason in the heart of Liverpool's defence. Inexperienced yet cool on the ball and strong defensively, Wisdom could now find himself called upon more often than would be expected.
Rodgers had suggested on Liverpool's official website that Wisdom could be loaned out this term, but it is more probable that he will be a regular member of the squad now this term.
Martin Kelly, meanwhile, is continuing his recovery from injury in the Under-21s and will be a further few weeks before being considered for first-team action.
Both players can fill in on the right side of defence or in the centre, but both also have limited experience in that key centre-back role at first-team level.
On the pitch and possible outcomes
Agger needs a long-term partner. Kyriakos Papadopoulos is widely acknowledged as Brendan Rodgers' preferred target for the job, with the Daily Star reporting the Reds are closing in on the Schalke man, but for this year it might mean Toure is a regular starter. Skrtel neither fits the requirements nor appears to be in Rodgers' plans, but his wages and market value are both too high to leave him on the bench for another entire year.
On the other hand, if Liverpool cannot bring in reinforcements this summer, can they afford to let their only other senior centre-back leave?
Coates will not be available until into the new year at the earliest, meaning Wisdom and Kelly would be required to feature in cup matches and fill in when required in the Premier League.
It's going to mean one of two things for the Reds in the transfer market: being forced into spending on a player Rodgers did not initially want for the long haul, or else retain Skrtel, a player he doesn't want and would prefer to cash in on.
Neither are ideal, but if Toure or Agger suffer injuries or suspensions, Rodgers will come under scrutiny for not securing further reinforcements if Wisdom or Kelly do not prove up to the job.
Having only two senior central defenders also robs Rodgers of the possibility of using one of his occasional tactical switches—moving to a back three—with any regularity, especially while Kelly is not yet fully fit.
Furthermore, despite the addition of Aly Cissokho to left-back, if the Reds are required to use either of Wisdom or Kelly in the centre, the team will then be lacking options on the right side of defence as cover for Glen Johnson.
Coates and Skrtel were both likely to leave the Reds this summer as Rodgers restructured his back line, but the injury to the former and the lack of a first-team replacement for the latter has left the defence looking a little unbalanced and lacking in depth.
The positives for Rodgers to stick with are that the "preferred" back four kept several clean sheets in preseason and the opening Premier League game, and also that, with no European football to contend with this season, the main starters should be able to remain fit for most league fixtures.
It might now take an extra year to get the defence the way the manager wants it, but at this point he has a big decision to make over the future of Martin Skrtel in particular, hampered and confused because of Coates' long-term injury.