Deeney spent two months behind bars in 2012 for an attack on a group of students in Birmingham.
The forward had his wages suspended by Watford and Mariappa stepped in to help his family with a £10,000 loan.
Mariappa said: “It is what you do for someone you care about. He was going through a tough time.
“I used to write to him and spoke to him a few times. He asked me to do something and I did it as I am sure that he would have done the same for me."