From United's website:
Zieler arrived at Carrington on Friday afternoon with his parents to sign scholarship forms with the Reds.
Les Kershaw is Academy Director at Manchester United, and he explained to this website the process for bringing Zieler to the club.
"We have a scout based in Germany called Peter Braund," explains Kershaw. "Peter watched him play and recommended the boy to the club.
"He was then watched by our goalkeeping coaches and FC Cologne allowed him to come here for a period of assessment.
"We liked what we saw.
"He will join us this summer, on 1 July. It's a scholarship scheme - the scheme offered to all 16-year-old boys who come to the club."