Barcelona have been relatively quiet in the summer transfer window so far.

The Catalans have only made one signing this summer in the form of Jordi Alba and it has been reported that the club are still looking for a defensive minded player.

In this article, we'll have a look at the five best possible targets that Barcelona should aim to buy before the transfer window shuts down.

1. Lars Bender

Lars Bender is a versatile midfielder who plays for German club Bayer Leverkusen.

The German international starred in his nation's Euro 2012 win over Denmark in the group stage, scoring the winning goal and earning numerous plaudits for his industrious display.

With Tito Vilanova stating that the club is looking for a player who could play both as a midfielder as well as a defender, Lars Bender looks like a relatively safe bet and also a cheaper option than Javi Martinez, who has a £32m price tag on his head.  

Lars would not only appear as an able deputy for Sergio Busquets, he could also be able to provide adequate back up to Dani Alves at the right-back position and possibly Carles Puyol for the centre-back place.

2. Daniel Agger

It has been reported over the past few days that Barcelona are eyeing an audacious bid for Liverpool defender Daniel Agger.

The latter is a no-nonsense defender who can shut down the opposition in a matter of seconds and could go on to form an impressive partnership with Gerard Pique at the heart of the Catalan's defence.

He's been heavily linked with a move away from Anfield this summer and with manager Brendon Rodgers stating that Agger would be allowed to leave for the 'right price', Barcelona should surely test the waters with a bid of around £15m  for the Danish international.

However, one drawback of this move could be Agger's constant injury and fitness troubles that have only allowed him to make 165 appearances for the Reds in over seven seasons.

3. Alex Song

If the latest reports are to be trusted, Barcelona have agreed to personal terms with Alex Song and will discuss a transfer fee with Arsenal next week.

Even though his defensive duties might have been questioned and criticized at times, Song is a highly underrated, great holding midfielder with great vision, passing skills and ability to protect the back four.

The 24-year-old would have no problems fitting into Barcelona's system of play could he a huge hit at Nou Camp.

However, it would be interesting to see whether Arsene Wenger would allow another of his prized asset to leave the Emirates and join the more tempting Barcelona team.

4. Yann M'Vila

Well slightly an unrealistic options, Yann M'Vila is a 22-year-old defensive midfielder and arguably one of the most sought-after youngsters in world football today.  

The French international was apparently heading to the Emirates this summer, but latest reports have revealed that the deal has been called off as the Gunners have apparently turned their attention to Real Madrid's Nuri Sahin.

M'Vila posseses all the attributed of an ideal defensive midfielder- he sits in front of the defence, dictates the flow of the game from a deeper position, ventured forward at times to help the attackers and is most importantly, ready for a transfer this summer.

5. Vital Dede

Vital Dede currently plays club football for Brazilian club Vasco da Gama, where his impressive performances have earned him international recognition.

The 24-year-old is a highly consistent player possession great tackling abilities and a neat ball control and technique.

With Barcelona currently short on transfer funds, Dede could prove out to be an economical signing who could be a mainstay in Barcelona's defence for many years to come.

However, Barcelona could have to beat interest from several other European clubs like Milan and Manchester United, as they too are keen on the signature of the Brazilian.