Rumours of marriage have been circulating for McConaughey since Alves was spotted wearing a new ring during their visit to Paris last week.
The two enjoyed a romantic time in the City of Lights, where McConaughey is working on a commercial for Dolce & Gabbana.
The agent for the Texas star denies that McConaughey is engaged, but adds that the star will eventually marry.
McConaughey, 37, is currently starring in the film Tropic Thunder. He will also be starring in the romantic comedy Ghosts of Girlfriends Past, which will open in 2008.