Blind is one of the players linked with a move away from Old Trafford this summer, but Alderweireld has suggested the Netherlands international would be welcomed back at the Amsterdam ArenA.
"Daley is a great guy. We did not just play together, but also went to school together. He is a proper Amsterdammer," he told De Telegraaf.
"It is nice for both parties involved that he has said he would be open to a return - if it happens."
Blind, who turned 28 in March, played over 100 Eredivisie matches for Ajax, scoring three goals in the process.
He left his hometown club in 2014 to move to the Red Devils and has subsequently played 90 Premier League matches, netting four times.
However, he has found his opportunities to impress increasingly restricted under manager Jose Mourinho and featured in only seven league matches last term and 17 matches in total, although he missed around three months due to an ankle injury.
Alderweireld, meanwhile, spent nearly a decade with Ajax earlier in his career and has been linked with a move to United this summer.
A return to Ajax has also been floated, and the 29-year-old is not ruling out heading back to the club later in his career.
He added: "It's hard to look into the future, but a return to Ajax could be an option on the long term. I had a great time there."