The 20-year old Chilean striker has been on loan with the Croatian club since the summer but according to president Zoran Mamic, Zagreb have completed a transfer with the Red Devils which will begin at the end of the current campaign.
"We have bought him outright for 1m (£780,000)," he told Prensa.
"We have already signed a contract with him for the summer.
"There is no doubt it is ours and the deal is resolved."
Henriquez joined United from Universidad de Chile in 2012 but failed to make a senior appearance for the Old Trafford outfit who subsequently sent him on loan to Wigan Athletic and Real Zaragoza prior to his August shift to Dinamo.
Since arriving in Zagreb, the five-time Chile international has scored 10 goals in 15 appearances for the Croatian top flight league leaders.
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