The French government proposed senior diplomat Laurent Stefanini for the post in January but the Vatican is yet to respond to approve the choice.
The Vatican usually responds within six weeks to approve such a new ambassador.
The nomination of Mr Stefanini was seen as a litmus test for Pope Francis, who has taken a more liberal stance on homosexuality.
A French government spokesman said there had been negotiations with the Vatican over the appointment.
"France has chosen its ambassador to the Vatican. This choice was Stefanini and that remains the French proposal," said spokesman Stephane Le Foll.
Observers say most Vatican appointments are confirmed within six weeks and that this long silence should be read as a rejection.
The Vatican traditionally makes no statement if it intends to decline a nomination.
Mr Stefanini served in the Holy See as a deputy ambassador in the French embassy from 2001 to 2005.
He was described by the country's foreign ministry as "one of our best diplomats".
France legalised same-sex marriage in 2013, despite opposition from the Catholic Church.
Pope Francis is regarded as more tolerant of homosexuality than previous popes. "Who am I to judge?", he said in 2013.

The band's set at Seaclose Park will be their only festival show of the year.
The set on Sunday 14 June, which will close the festival, will include original member Christine McVie, who recently confirmed that she would be rejoining the band.
Festival organiser John Giddings told Newsbeat: "It's the best news I've had in a long while."
He said that he had been asking the band to perform at the Isle of Wight for the last seven years.
"Every year I have asked without fail," he revealed. "I'd like to tell you otherwise but it's true, I have begged them."
Previous acts to headline Isle of Wight Festival include The Who, the Rolling Stones and Paul McCartney.
Despite his years of asking the band to perform, John Giddings explained that he thought Fleetwood Mac, whose debut album Peter Green's Fleetwood Mac went to number four in the UK in 1968, didn't need much persuading.
He said: "If you're a band of substance, it [Isle of Wight] becomes part of your bucket list really."
Red Hot Chili Peppers, Kings of Leon and Biffy Clyro headlined the event this year.
Talking about choosing the rest of the 2015 line-up, John Giddings said: "The problem is when you're looking for some of the top acts in the world, there aren't that many of that calibre... without repeating yourself it becomes harder by the year."
However, the organiser did say there would be some newer acts named on the line-up.
"When we announce Friday and Saturday, you will see younger bands. It's an eclectic mix of past, present and future bands."
The organiser added that the other two headline acts of the festival would be announced soon.
Giddings agreed younger bands have the ability to sell festival tickets as well as older bands like Fleetwood Mac and Lionel Ritchie, who has been named as the first act on the Glastonbury 2015 line-up.
He said: "I think younger bands of course can do it as well, but the golden age of rock and roll is past.
"The music is different now whereby you can download individual songs on iTunes and it becomes hard to name the lead singer of Bastille or Imagine Dragons."
He said "there are lots of groups out there" but added "who is the biggest act out of England that have toured stadiums in the last five years? One Direction.
"I think they'd rather be somewhere else than at the Isle of Wight festival."
However, John Giddings did say "there are great new bands out there" and referred to The Black Keys and Royal Blood as "incredible".
The Isle of Wight organiser was recently quoted as calling Ed Sheeran "boring" having suggested "we're (the UK) not building headliners any more".
He told Newsbeat that "he's jolly good fun" and after saying he'd recently met the 23-year-old added: "He's selling tickets and he's selling records and we should all be grateful for his existence."
Tickets go on sale on Friday at 09:00 GMT
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France has said it will not back down over its nomination of an openly gay ambassador to the Vatican.
[NEXT_CONCEPT]
Fleetwood Mac have been announced as the first headline act of Isle of Wight 2015.