The Reds are said to be interested in signing Marlon, Nili Perdomo, Marc Cardona and Wilfrid Kaptoum, all of whom play for Barcelona's second string.
Chief Spanish and Portuguese scout Kiko Espinar is reportedly keeping a close eye on their progress, but Barcelona are said to be determined to keep their young stars, after losing the likes of Hector Bellerin, Cesc Fabregas and Gerard Pique to English clubs at an early age.
Cameroon midfielder Kaptoum is the only one from the quartet to make an appearance for the first team, with a goal in the Copa del Rey semi-finals against Valencia, as well as featuring for Bayer Leverkusen in the Champions League last season.