"From what I've read, it doesn't look very likely to me," he told reporters when asked about media reports that a land dispute in the Cancun region could prevent the circuit from being built.
"But I wouldn't be surprised to see a race in Mexico within the life of the current Concorde Agreement, before 2008."
Local organisers announced last October that the Caribbean resort would host a race for five years starting in 2006, marking the country's return to the calendar for the first time since a Grand Prix in Mexico City in 1992.
India has also been interested in hosting a Grand Prix in Hyderabad, although a recent initiative foundered after the chief backer of the project was voted out in regional elections last year.
However, the arrival of the country's first Formula One driver, Narain Karthikeyan at Jordan, has revived talk of a future Indian race.
"It depends on the local politicians," said Mosley. "One minute there is great excitement and then they lose the election and it goes away again. I suspect that if Karthikeyan goes well, then you will see one in India."
This year's calendar is already an unprecedented 19 races and Mexico would have been a 20th unless one of the European venues was axed.
