The guide was attacked on Monday after the group left their vehicle to inspect a pride of lions with cubs under a tree in the Hwange National Park, the country's largest natural reserve.
"Some cubs came near the tourists and one adult lion identified as Nxaha charged at them," police spokeswoman Charity Charamba told AFP.
"The adult lion retreated for a while and then came charging at the guide. It knocked him down and mauled him on the neck and shoulder.