The seven-times champions have lost their last four games in all competitions, their worst losing streak since they became the measure of all things in France in 2002.
After they were knocked out from the French Cup and the Champions League, they only just held on to top spot in the table after being stunned 2-0 at home by mid-table Auxerre last week.
Lyon, on 53 points, benefited from Paris St Germain's 3-1 home defeat by arch rivals Olympique Marseille, who moved up to second, just one point off the pace and ahead of the capital side on goal difference.
"We wanted to get a new impetus but we failed. We are tired physically and mentally but we must overcome our disappointment. Great teams sometimes have to go through hard times," Lyon chairman Jean-Michel Aulas told reporters after Sunday's defeat.
Sochaux should be easy prey for the leaders as the eastern side are just above the drop zone. But they have won three of their last four league games and they notably beat Marseille last month.
INJURY WORRIES
Lyon are still hampered by injury worries, especially in defence.
France centre back Jean-Alain Boumsong and Ghana's John Mensah did not train this week while Francois Clerc has only just come back from a seven-month absence and Brazilian Cris will be suspended against Sochaux.
Lyon's troubles have given hope to their rivals, who were unused to still vying for the Ligue 1 crown with 10 games to play.
"We are still in the race and it is going to be very tight until the last day," Marseille coach Eric Gerets told reporters.
Marseille host Nantes on Saturday knowing they could overtake Lyon at the top for a day at least, while Paris St Germain visit fifth-placed Toulouse on Sunday.
The capital side will welcome back playmaker Stephane Sessegnon, whom they sorely missed through suspension against Marseille.
"Each time we suffered a setback this season, we managed to get over it," PSG goalkeeper Mickael Landreau told reporters.
Girondins Bordeaux, who are fourth on 50 points, visit bottom club Le Havre on Saturday.
