The teenager was believed to have undergone a medical in Manchester on Tuesday, although it has been claimed in Chile that he will be immediately loaned back to his current club, Universidad de Chile.
United are yet to make any announcement on the subject.
However, Henriquez is regarded as one of his country's brightest prospects.
He impressed at the recent Milk Cup tournament in Northern Ireland, when Chile finished third in the six-team elite competition.
Source: PA
Source: PA