World number one Novak Djokovic and seven-time consecutive title holder Rafael Nadal will head the field for the April 15-22 Masters 1000 in Monte Carlo, but Roger Federer will be missing.
"We're keeping a wild card to one side for Roger," tournament organiser Zeljko Franulovic said of the Swiss world number three.
"You never know, even if he has played a lot since the start of the season. He's decided in the past to come at the last minute."
Should Federer be absent, the six other players in the top seven are expected to be there.