Finlay has cerebral palsy and recently he sent a letter to his hero, revealing how the midfielder's close relationship with his younger sister Holly, who also has the condition, has been inspirational.
"I wish there were more people in the world just like you who treat people with disabilities the same as anyone else," Finlay wrote.
"It makes me really happy when I see you, a famous footballer, know what it's like to live with people with cerebral palsy."
And after one such session, Finlay was stunned to receive a surprise visit from his hero, who had replied with an emotional letter of his own as well as a signed City shirt.
"I want to say a big thank you for the letter you wrote to me," Grealish told Finlay. "It really touched me."