Roy Carroll believes Olympiakos can capitalise on his former club Manchester United’s problems at the back and feels David Moyes’ side are far more fallible than previous Old Trafford teams.
The Northern Ireland international, who played for United between 2001 and 2005, will be in the squad for the Greek champions and current league leaders for Tuesday’s first leg of their Champions League last-16 tie in Athens.
And Carroll, who played for Sir Alex Ferguson, feels the current United team are more fallible and fragile than their predecessors.
"They look nervous," he told the BBC. "Every time you watch them this season you just feel that the opposition will score. It's weird -- you don't associate that with Manchester United."
Carroll said Olympiakos have been looking to exploit United’s inability to field a settled back four as they look to inflict an 11th defeat of the season on the Premier League champions.
"We have been working on United's defensive problems in recent days; that's what we have to do," he added. "You have seen all season that they have been chopping and changing at the back. As a goalkeeper I know the effect of not having a settled back four and we have seen that from United this year. It's a different back four every game."
United, who were champions in 13 of the past 21 seasons, languish in sixth place and Carroll did not expect such a swift decline after Ferguson retired.
He said: "I have been surprised by their form this season.
"It's nearly the same squad which won the league last year but a new manager was always going to be a huge change, no matter who they appointed.
"Results haven't been going well, or the way you would expect, and it is tough for them."