The Argentine, signed by Dennis Wise for £10million in August, was expecting a crack in Europe – not a relegation dogfight.
"When I joined I never thought they were in danger of relegation, having to win win their last two home games to stand a chance of staying up," said Collocini.
"I was sold a club that would challenge in the top half with a good chance of doing well in the cups.
"But the reality is we're in the relegation zone and have to fight to get out of it. We must show we're ready to fight to stay up."
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Latest Toon boss Alan Shearer dropped the 27-year-old defender for last month's trip to Stoke after a dip in form, but the Argentinian understands the manager's reasoning – and doesn't doubt his commitment.
"Alan left me out and I had to accept it," he said. "I just had to work hard to get back into the team.
"The boss feels the pain more than anyone as he has been at Newcastle for so long. He was brought up here and is a fan.
"He wants us to be feeling like the fans are feeling. He wants us to share his passion and know how vital these games are."
Newcastle host fellow drop-zone dwellers Middlesbrough tonight, in a game Shearer has described as "the biggest game I've been involved in."
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