The Real Madrid boss says he would look to strengthen other positions in the squad rather than acquiring the Barcelona star.
The Portuguese has received widespread acclaim for his performances this season, including a stunning hat trick for his country in the second leg of its World Cup playoff with Sweden, which sealed its place at Brazil 2014.
The 28-year-old has also excelled at club level and is a firm favorite to lift the Ballon d'Or in January, and Ancelotti says he would strengthen in other positions of his side rather than bring in the Argentine to the Bernabeu.
"If I could sign one player for Real Madrid, it wouldn't be Messi, I'd rather reinforce another position," he told Italian broadcaster Radio Capital. "We have Cristiano, who needs Messi? God gave him [Ronaldo] a special gift."
However, Ancelotti did joke that the capital outfit might be interested in bringing Messi to the club should Barca decide to sell the Argentine.
"If Barca sell Messi, they should call us," he joked.