Clifford, who has won 21 international caps for the Republic of Ireland at Under-17, U18 and U21 level, has made six appearances for the Magpies.
He is in his third full season with Chelsea and was captain of the team that won the FA Youth Cup in 2010.
Clifford spent time at Plymouth earlier this term
but the deal could not be extended
because of their transfer embargo.
Source: BBC Sport
Source: BBC Sport