Manchester United fans have been urged to "take good care" of new signing Donny van de Beek in an open letter by their former player Edwin van der Sar.
The Ajax chief executive also asked the United supporters to "help him dream".
"Like you, we pride ourselves on being one of the best at developing young talent and giving young players a shot at the highest level," he said.
Netherlands midfielder Van de Beek completed a £35m move to Old Trafford from the Eredivisie side on Wednesday.
In the letter, which was also published as a full page advert in the Manchester United Evening News, the former Netherlands goalkeeper added: "You could say your new star is the embodiment of that pride.
"That's one of the many reasons we don't like to see him leave, but we understand it's time for him to move on. To dream on.
"And where better to do so than in your theatre. Trust me, I know.
"Please take good care of our Donny, and help him dream."
Van Der Sar made 266 appearances for Manchester United between 2005 and 2011, winning 10 trophies, including four Premier League titles and the Champions League in 2008.
After retiring from playing in 2011 he returned to first club Ajax as marketing director in 2012, becoming chief executive four years later.