The 21-year old left Hamburg to join Bayer Leverkusen in June but his representative Thies Bliemeister has revealed the reasons for the speculation surrounding a potential shift to Old Trafford.
"Even United wanted Sonny,” he told Bild.
"Manchester United was very interested in him. We had already held talks. HSV to Manchester had also been reported.
"The interest was a great honor for Son. But Leverkusen has simply the best impression made. And as an intermediate step, Bayer is ideal for his career now."
Son, who will get the chance to take on United in the Champions League on September 17, has scored two goals in five appearances in all competitions for Bayer thus far.