Decisions from the UEFA Club Financial Control Body (CFCB) Investigatory Chamber are due by the end of the year, with the four clubs to be investigated for overdue payables.
Acting chief investigator Umberto Lago is to lead matters, with 37 clubs having originally been asked to submit further information regarding any overdue payables towards other clubs and employees as well as social/tax authorities.
Bursaspor, Ekranas, Cluj and Astra will now be investigated further as part of UEFA Club Licensing and Financial Fair Play Regulations.
"The UEFA Club Financial Control Body (CFCB) Investigatory Chamber, headed by the acting chief investigator Umberto Lago, has announced that four clubs participating in the 2014/15 UEFA Europa League have been referred to the CFCB Adjudicatory Chamber, due to breaches of the monitoring requirements," read a UEFA statement.
"In particular, important overdue payables towards other clubs, employees and social and tax authorities as of 30 June and 30 September 2014.
"The CFCB's final decisions are expected to be taken by the Adjudicatory Chamber before the end of the year."