Mane had to leave the pitch after 20 minutes of Bayern's 6-1 win over Werder Bremen on Tuesday.
The forward will be key to Senegal's hopes at the World Cup, where they face the Netherlands in their Group A opener on November 21st, followed by hosts Qatar and then Ecuador.
"Sadio Mane was hit on the leg, which caused him a little nerve pain. Nothing too serious and his participation in the World Cup should not be in jeopardy," Toppmoeller told reporters.
Bayern coach Nagelsmann said the two-times African Footballer of the Year would undergo scans on the injury.
"I can't say anything for sure, he took a blow to the head of his shin. That's an unpleasant spot, it radiates a bit into the muscles," Nagelsmann said.
"I think he has to go to the X-ray to see if there is something there because it is splintering easily. But I hope that nothing is wrong. I can't say anything for sure yet."
Mane is a key player for Senegal, who will face the Netherlands in their Group A opener on November 21. They will also take on Ecuador and hosts Qatar in Group A.
Mane scored the winning spot kick for Senegal as they beat Egypt on penalties to earn their first Africa Cup of Nations final in February.
Senegal manager Aliou Cisse is due to announce his World Cup squad on Friday.
