Dutchman Louis van Gaal revealed in a Spanish press conference that he was on the lookout for a left back following the departure of Sergi to Atletico Madrid.
Celta Vigo's Juanfran and Juan Pablo Sorin, a recent recruit at Lazio, have been touted as possibilities but Argentine star Placente is said to be the number one target.
The pony-tailed defender helped Leverkusen to the Champions League final and his raids down the left flank were a real source of danger for the opposition.
Bayer are reluctant to let their £4 million capture from River Plate go - especially after the departures of Michael Ballack and Ze Roberto - but face a fight to hang onto the South American ace with Barca ready to open the chequebook.
Van Gaal is attempting to stamp his authority on Barcelona in his second spell at the club and has already rung the changes with the signing of Juan Roman Riquelme and the release of Rivaldo.
