That valuation looks ridiculously low for a player, who signed for Celtic when he was just seven and who has come through the ranks and developed into a star performer and one of Brendan Rodgers' prized assets.
Celtic are likely to contest any interest in their young left-back but may struggle to fend off the financial muscle of United.
He told The Times: "I'm not thinking about anyone other than Celtic just now".
"I'm enjoying my career here".
The Hoops' record transfer fee received was £12.5million earned from Victor Wanyama's sale to Southampton in 2013.
The English Premier League giants have been linked with Celtic's impressive full-back throughout the season with Old Trafford scouts said to have recommended him to manager Jose Mourinho.
Tottenham, Everton and Newcastle have all been linked with the former Southampton star following his hard four years at Old Trafford.