Olympiakos goalkeeper Roy Carroll has warned former employers Manchester United their turbulent season could suffer another blow when they arrive in Greece on Tuesday.
Carroll, who spent four years at Old Trafford, claims the recent woes of United under David Moyes gives the Greek champions hope heading into their European showdown.
United beat Crystal Palace 2-0 at Selhurst Park on Saturday but remain 11 points shy of fourth-placed Liverpool in the Premier League.
Carroll admits a lack of form from the defending English champions proves they can be beaten and insists Olympiakos are ready to add further misery to Moyes' first season at the helm.
"It's been a difficult season for United in the Premier League," Carroll told the Daily Mirror. "They used to score goals late on to win games, now they're conceding goals late on to lose games or drop points.
"That gives us belief; that even the best teams - like United - can be beaten. That's the way we're looking at it, with United not in the best of form at the moment.
"It's important for us to get something from the first leg to take to Old Trafford. We must get some sort of result at home first."
The 36-year-old is unable to put a finger on the reason behind United's domestic failures, but warns writing them out of European contention would be a mistake.
"I don't know why they've struggled so much in the Premier League, but we know how good they still are on their day and won't underestimate them," he added.
"They won their Champions League group quite easily, but in the Premier League, if you make any kind of slip-up, it can lead to a goal against you, as we've seen with United this season.
"It's great for the Olympiakos fans to have United coming here. The situation over here [with Greece's failed economy] isn't great, but United coming over here keeps people's minds off it.
"They're so passionate over here. There may only be 32,000 fans in the stadium, but the noise from them will make it seem like there are 100,000 in there."
Despite United's sufferings this season, Carroll does not expect them to endure a similar decline to rivals Liverpool, who have not won the league since 1990.
"For years, Liverpool were one of the best teams, winning European Cups and league titles," said the Northern Ireland international. "Then it all stopped for them, but I don't see the same thing happening to United.
"Okay, this season has been tough and they might miss out on the Champions League at the end of it. But I think they'll be back stronger next season. I don't think they'll drop like Liverpool did. I hope not, anyway, because United are a fantastic club and I had four great years there.
"No matter who came in after Sir Alex Ferguson, it was always going to be tough. Sir Alex is a legend all over the world, not just in Manchester. But everybody knows what David Moyes achieved at Everton with hardly any money, so he's already proven himself as a manager."
Since the arrival of Roberto at Olympiakos, on loan from Atletico Madrid, Carroll has made just one appearance, but despite being out of favour the goalkeeper is eager to earn a contract extension.
"This season has been difficult for me and things have changed completely for me," he said. "We've brought in a new Spanish keeper who's done really well, so I can't have any complaints.
"At the moment I'm just biding my time. I'm out of contract this summer and I hope to stay with Olympiakos, but I'll just have to wait and see what happens.
"I'm hoping to get another season here, because my family and I are settled in Greece. The club have been really good to me, but you never know what can happen."
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