One topic looks set to dominate the January transfer window: whether Arsenal will sign the defender they so clearly need. When Thomas Vermaelen departed for Barcelona in August, Arsenal were left with just six senior defenders. With two of those -- Kieran Gibbs and Nacho Monreal -- left-backs, it meant just four players to fill the three positions at center-back and right-back. Without major fitness problems, the situation was barely manageable, but, as has been all-too familiar for Arsenal in recent years, the injuries have been frequent.

Indeed, only Per Mertesacker has remained fit throughout the campaign. Mathieu Debuchy and Laurent Koscielny have both had extended spells out of the team, meaning Monreal has had to deputize as an unconvincing center-back. Manager Arsene Wenger has conceded that another defender would be quite useful in January, although has cautioned that signing players in January is no easy task.

He has a point. With clubs pursuing their own objectives and reluctant to sell their best talent, players hesitant to up sticks midway through a campaign as well as the complication of Champions League ineligibility, January is not an ideal time to procure top talent.

Moreover, the examples of central defenders arriving in January and making an instant impression at top clubs are rare. Nemanja Vidic’s transfer to Manchester United in 2006 is one of the most famous examples of an astute January signing, but it took the Serbian until the following season to adjust to the Premier League. Gary Cahill, who moved within the Premier League -- from Bolton to Chelsea -- and four months later lifted the Champions League, was a more immediate success.

But the absence of top-quality defenders around the world currently makes Wenger’s task even greater. Mats Hummels, despite a tough start to the season, is at the top end of defensive talent and has been frequently linked with Arsenal, yet it is a deal hard to imagine taking place next month. Currently bottom of the Bundesliga, Borussia Dortmund cannot afford to be seen to be giving up on their season by selling off yet another top player. It would take stupid money to convince them, and Arsenal, simply, do not pay stupid money.

While Arsenal have loosened their purse strings in the past couple of years, Wenger has historically not spent big on defenders. Indeed, his record fee paid for a defender was the reported £12 million committed on Debuchy this summer. The most spent on a center-back is just £10 million. Cutting through the myriad of rumors, here then are three defenders Arsenal could realistically sign in January.

Tyrone Mings (Ipswich Town)

The 21-year-old would in many ways be a typical Wenger signing: he is young, would be largely unheralded and appears earmarked for a different position than the one in which he has established his reputation. Mings have earned rave reviews as an attack-minded left-back in the Championship, yet there is much speculation that Wenger is prepared to pay £8 million based on his potential in the center of defense. Still, with Ipswich chasing promotion to the Premier League and Mings having stated that he would have little interest going to a big club only to sit on the sidelines, doing a deal in January may prove complicated.

Virgil van Dijk (Celtic)

The 23-year-old received his first call up to the Netherlands squad earlier this season and his form for Celtic continues to spark speculation that it is only a matter of time before he moves south of the border to the Premier League. Celtic coach Ronny Deila has urged the former Groningen man to see out this season and battle for trophies, while cautioning suitors that he will not come cheap. Yet, with Celtic having crashed out of the Champions League before the group phase and with Scottish domestic soccer at a low ebb, he would surely be tempted by the prospect of a transfer to rumored suitors Arsenal.

Matija Nastasić (Manchester City)

Cases of players between moving between top clubs in England are still rare, but there is little to suggest Manchester City would have any hesitation about letting their Serbian defender head to Arsenal. After an impressive debut season following his transfer from Fiorentina in 2012, Nastasić has dropped off the radar spectacularly, initially through injuries and then having simply falling out of favor. He last played for City in August’s Community Shield against Arsenal. Around that same time, it was widely reported that Arsenal were interested in signing the center-back after he was shopped around by City. His high wages may have ended those hopes at the time, but, still aged 21 and clearly with substantial natural ability, he could be worth pursuing again in January. Admittedly, though, his injury history should raise alarm bells for a team that already has a consistently full treatment room.