Ideally Arsenal would like a replacement along the back line before their fixture with Manchester United, but Arsene Wenger has to add someone if Arsenal want to stay in the top four.

Wenger must sign a defender before the end of the transfer window for the Gunners.

Arsenal have suffered several injuries along their back line throughout this year's campaign. It has reached the point of desperation with the likes of Francis Coquelin filling in at left-back.

The Gunners sit five points behind Chelsea with a game in hand but must sure things up if they want to catch their London rivals.

Manchester City: Wayne Bridge

Wayne Bridge has fallen out of favor with Roberto Mancini. Arsene Wenger should make a move for the 31-year-old left-back.

Bridge has experience in the Premier League and could likely be taken on loan.

Mancini commented on Bridge's future and Manchester City's need to sell players.

"We need to sell three or four players and with Carlos we could close [a deal] with a club in the next three or four days, and also possibly Wayne [Bridge]."

If City is open to loaning Bridge out until the summer, Wenger may be enticed to bring him in as fire insurance.

Ajax: Jan Vertonghen

The Ajax defender has drawn the attention of several clubs in England with his play in Amsterdam. Jan Vertonghen's experience is one of the main appeals.

Vertonghen has played in the Champions League and has 35 caps under his belt for Belgium. He's also won a Dutch league championship as the 24-year-old eyes a move to the Premier League.

Arsenal would benefit immensely from adding a defender like Vertonghen. The Belgian could be used as a utility defender and help Arsene Wenger patch any holes along the back line.

He also brings an added maturity to the squad having been a captain for Ajax. According to the Metro, the defender is rated at £10 million by the Dutch club.

Olympique Lyon: Aly Cissokho

Lyon could lose one of their star players in defender Aly Cissokho by the end of the January transfer window. Arsene Wenger has a fixation with Ligue 1 players and Cissokho fits the bill.

Cissokho was on the verge of a move to Anfield during the summer, but could be moving to the Emirates if Wenger decides to buy reinforcements for his defense. According to Sporsvibe, Arsenal will challenge Liverpool for the signing of Lyon's star left-back.

Arsene Wenger could swoop in for the left-back whose price tag has been valued at £16 million by the French club, but Arsenal could take the player on a loan-to-buy deal.

Cissokho could end up being the full-back that reminds supporters in North London of Ashley Cole.

Everton: Leighton Baines

Admittedly, the likely hood of this transfer would be quite a stretch. Leighton Baines could arguably be the best left-back in English football and he wouldn't come at a cheap price.

Baines would be a permanent answer at left-back for the Gunners. The 27-year-old Englishman would help secure a shaky back-line for Arsenal.

The selling point for Baines would be that he is in the prime of his career and could move to one of England's biggest clubs. Arsene Wenger may want to utilize Mikel Arteta to help recruit his former colleague.

Wolverhampton: Stephen Ward

Stephen Ward may not be the name most would want to see make a move to North London, but he could be serviceable for the Gunners. The Irishman has been a staple for the Wolves back-line.

Ward has adequate experience in the Premier League and wouldn't require transition time like Jan Vertonghen or Aly Cissokho.

The Irishman has started 21 games for Wolverhampton this season. Ward has netted three goals and has a fairly clean discipline record with only one yellow card.

Arsenal could look to take him on loan and get him on the cheap if he works out.

Justin Sparks is a Featured Columnist for Bleacher Report @JustinSparks22