Writing on his Instagram page after Leeds' season-ending 1-1 draw with Preston, the 31-year-old said it had been an "honour and privilege" to play for United.
Antenucci - who scored 19 goals across the two seasons - is out of contract and his family live in Italy where he is expected to return.
"It has been an honour and a privilege to have worn this historic t-shirt and having trod on Elland Road," he said.
"I always wanted in my career to play one day in England and I can say with certainty that this is the best club I could choose. This was a incredible lifetime and football experience."