Carried out by PricewaterhouseCoopers (PwC), the study revealed the institutions are carrying more than â¬1.3 trillion ($1,885 billion) in such tie-ups - and it will take them the next decade to try and run them down or sell them off.
The investigation showed that the amount calculates at â¬2,600 for every person within the European Union.
Authors of the report stated: "As well as price, the high degree of strategic analysis and data due diligence required in a more circumspect business climate is significantly slowing things up."
PwC highlighted non-performing loans as another challenge, with these deals totalling â¬225 billion in Germany last year, followed by Britain at â¬175 billion.
The European Banking Authority recently suggested its stress tests for banks on the continent are likely to be more stringent than they were in 2010.
By Claire Archer