This season, he has been the dominant player on clay, winning 17 straight matches on his favourite surface and three consecutive titles before Thiem halted his run in Rome last week.
"Rafa, next to Roger (Federer), has been the best player this year in terms of results", Djokovic said. "Their level of tennis is quite fantastic". The two best players in the sport aren't in Paris, injuries are affecting the one-time favorite and no one has pushed to the front of the pack in the lead-up to the clay-court major.More news: Milner warns signings not to disrespect Liverpool by joining for Champions League
A year ago, the Spaniard appeared to be rounding into form in Paris when he was forced to withdraw in the third round with a left wrist injury - the source of power for his vicious, whirling southpaw forehand that is so hard to counter on clay. "I started to feel a bit sick", the Scot told a news conference on Friday.
If the seedings works out, the World No. 1 will face former champion Svetlana Kuznetsova in the last eight with Muguruza locking horns with Dominika Cibulkova.
"It's an awesome feeling to be back and to look at this trophy. It brings back memories from previous year", Djokovic said at the draw ceremony.More news: Celtics' Brown questionable for Game 5
Two-time French Open victor Maria Sharapova is missing because tournament officials denied the 30-year-old Russian a wild-card entry following her return from a 15-month doping ban in April.
Halep has an ankle injury and described her chances of making Roland Garros as "50-50" earlier this week. Raonic, who's in the bottom of the draw in the same half as defending champion Novak Djokovic, will open against world No. 38 Steve Darcis of Belgium.
That includes six matches in the men's singles and six in the women's singles.
Williams is not playing because she is pregnant, while Sharapova's ranking wasn't high enough to gain direct entry into the tournament after a 15-month doping suspension.More news: LeBron, Cavs try to shake 'weird' loss in Game 3 to Celtics
"Of course we're both hoping that this can bring success on the court, but finally, it's, you know, an opportunity for us to, as I said, to really grow and evolve, first of all as human beings and as tennis players, and that's all I'm focused on at the moment, right?"