Vandals broke into a van carrying CSKA fans from the Executors club in Haskovo, journalist Tihomir Petkov told BTA.
Late last night, someone smashed the side window of the van near the Crystal City hotel in Athens, where the CSKA fans are staying. Documents and a jacket were taken.
The case has been reported to police, who are investigating.
Petkov is travelling with the fans, who are in the Greek capital for CSKA's Conference League match against Panathinaikos today.