Leaders Paris Saint-Germain are five points clear at the summit ahead of their clash with Marseille on Sunday, leading Ranieri to admit defeat in Monaco's quest for top spot.
Having seen star striker Radamel Falcao ruled out with a long-term knee injury, the Italian feels this season's championship is PSG's to lose.
"We did not lose the trophy because we lost here (at Saint-Etienne). Only PSG can lose the trophy. Paris can win Ligue 1 by playing at 100 per cent. We have to play at 130 per cent and win all of our games, which is impossible," he said.
"PSG won the trophy at the start of the season, not now."
Goals from Fabien Lemoine and Romain Hamouma helped Saint-Etienne to victory at the Stade Geoffroy-Guichard as Monaco were beaten for the first time since December 20.
Ranieri conceded Saturday's opponents, who are now eight points behind Monaco, deserved their win.
"Before we went 2-0 down, the performance of my players was good. Then we got two or three chances to at least to level the score, after the great goal of Lemoine," he continued.
"It's been two months in which we did not lose a game. When Saint-Etienne scored the first goal, we started to get frustrated, with a lack of precision, playing too fast. Saint-Etienne deserved their victory."
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