The La Liga champions were banned from registering players for two transfer windows by FIFA due to a transfer irregularity. The Ban ended on August 31 d so the only reason they cannot now register them is because no club can register players until the transfer window reopens in January.
However, there is an exception to this rule is if a club loses a player through injury for longer than five months. According to ESPN, Barcelona have asked for permission to register Turan replace the injured Rafinha.
The reigning La Liga champions signed Turan on a £24 million transfer from Atletico Madrid over the summer
Speaking to Sport former Barcelona president Toni Freixa claimed that the club have already served their transfer ban and could ask for a permit under Article 123 of the Spanish Football Federation’s law book.
“FIFA sanctioned Barcelona for two transfer windows, last winter and this summer, and they’ve since passed,” he told Sport.