Milla this week told AFP that Eto'o had "brought lots to Barcelona and Inter Milan but never anything to the Cameroon team".
"It's also a question of discipline. Cameroon is waiting for him to react," Milla said.
Eto'o, who this month won the Champions League with Inter to add to his two European Cup winning medals with Barca in 2006 and 2009, dubbed Milla "bitter".
"Is it worth me going to the World Cup?" he asked on the sidelines of an exhibition match in Paris.
"I've still got some days to think about it but I'll see if my taking part is important because I don't need this in my career."
Speaking to Canal Plus television channel, he added: "It is always before tournaments that bitter people wake up.
"What has he (Milla) done? He hasn't won the World Cup. They played in a quarter-final (in 1990) and with what a team. They had one of the best teams with some great players throughout. It's not because they knew glory at the age of 40 that they can talk.
"And then you wonder, 'are they my people?'. Are they really my people? Is it really worth going to the World Cup?"