The mayor of Lorient Fabrice Loher confirmed the news after widespread reports in French media of the death.
"A member of the contracted pitch maintenance team working for the club died after the accidental fall of a heat lamp," the city said in a statement.
It was Rennes substitutes who raised the alarm as they were still on the pitch when the accident took place.
Players and medical staff were seen on television rushing back out to the pitch to help, and were shortly joined by a team of fire fighters.
Some remained on the sidelines in shock as rescue workers tried to save the man, reportedly a 38-year-old father of three.
He was transported to a local emergency unit but did survive.