Sir Alex Ferguson signed the highly-rated forward earlier this season and he believes he has a big future ahead of him at Old Trafford.
United are willing to loan Manucho out as he is well down the pecking order at Old Trafford and they want him to gain valuable first-team experience at Panathinaikos.
A number of clubs from Portugal, Italy and Belgium are believed to have asked for Manucho, but Carlos Queiroz's good relationship with Pana boss Jose Peseiro has seen the Greeks win the race for the striker.
Manucho, who has impressed at the Africa Cup of Nations with Angola scoring three goals, confirmed he will be making the move to Athens when he returns from the tournament.
"After the ACN I will return to Luanda and then head to Athens," Manucho told Angola tv . "I am looking forward to playing in Greece before hopefully being a success at Old Trafford."