Celtic have said that they are not looking to off-load the centre-back, but Newcastle could make an offer before the end of the transfer window.
McManus, 25, made his debut for Celtic in 2003 and was made club captain after the departure of Neil Lennon in May 2007.
He has made 17 appearances for Scotland and has captained the national team during the absence through injury of midfielder Barry Ferguson.
Celtic have been exploring options to fill their left-back berth, although Strachan has stated that he would be happy to see out the remainder of the current campaign without adding further to his squad.
Former Newcastle manager Sam Allardyce brought Jose Enrique to Tyneside on a five-year deal from Villarreal in August 2007 for a fee of £6.3m.
The 23-year-old has represented Spain once, against Georgia, when he scored the only goal and was also sent-off in his country's 1-0 European Championship qualifier win.
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