The incident took place outside Stadium 974 in Doha on Monday after Brazil's 4-1 win over South Korea in the round of 16.
Videos making the rounds on social media show Eto'o appearing to kick the photographer in the head.
The former Barcelona and Inter Milan striker is initially seen posing for photographs with some fans shortly before the incident occurs.
Eto'o has clarified that the victim is most likely an Algerian fan who tried to reopen old wounds with regards to Cameroon's World Cup play-off victory over the North Africans earlier this year.
"After the Brazil-South Korea match, I had a violent altercation with a person who was probably an Algerian supporter," Eto'o wrote on his social media channels.
"I would like to apologise for losing my temper and reacting in a way that does not match my personality. I apologise to the public for this unfortunate incident."
"I pledge to continue to resist the relentless provocation and daily harassment of some Algerian supporters," Eto'o added in his statement.
"Indeed, since the Cameroon-Algeria match, I have been the target of insults and allegations of cheating without any evidence.
"During this World Cup, Cameroonian fans have been harassed and pestered by Algerians on the same subject."
