Relegation-threatened Livorno have sacked Domenico Di Carlo after just 88 days in charge and re-appointed Davide Nicola.
Virgil van Dijk claims he knows nothing of interest from English clubs and is keen to prove himself in the Champions League with Celtic.
The 24-year-old Northern Ireland international made his United debut as a teenager in the League Cup against Coventry in September 2007 and has now committed to the club until June 2016.
United confirmed his new deal this lunchtime, with manager Sir Alex Ferguson saying: "Jonny has risen through the ranks to become an integral part of the first-team squad. He has developed into a top player for us and has scored a couple of important goals this season too. I am delighted he has signed a new contract."
Evans added: "I'm delighted to sign my new contract. I am so proud to play for such a great club, and there's no better feeling than playing football in this team and winning games."
He added: "I would love to play here throughout the rest of my career."