Astori died in his hotel room this month ahead of Fiorentina's scheduled Serie A clash with Udinese, with a post-mortem identifying cardiac arrest as the most likely cause of death.
Viola star Chiesa, who could make his senior Italy debut against Argentina on March 23, acknowledges it has been a difficult few weeks but is determined to honour his late team-mate with his performances.
"There aren't words to describe what happened," the 20-year-old told a news conference. "It was an immense and unexpected tragedy.
"He was a really important team-mate for me. Over the past two years, he really helped me feel a part of the group. He gave me the right advice when I needed it.
"I miss him hugely, but I must now react after this difficult period, particularly for him. He wanted to see strong and determined players, who gave everything for the shirt and were 100 per cent committed."
Chiesa is looking forward to the prospect of facing Lionel Messi on Friday at the Etihad Stadium, having already met Cristiano Ronaldo on a football pitch in his brief career to date.
"I played against Cristiano Ronaldo at the [Santiago] Bernabeu and it was like it was make-believe," he said. "When you say 'Messi', you think of football. He has no defects. It will be exciting to play against him."