The co-hosts are expected to reach the last four at the DW Stadium, but McNamara believes that the French will provide a stern challenge, despite finishing third in Group B with a -63 points difference.
"I think France are going to be a really tough team," the England boss is quoted as saying by Sky Sports News. "They showed that and they stood up to Samoa.
"They were brave and pretty heroic at times under some real pressure. They have got a lot of spirit within their team, so they're dangerous opposition for us."
England made it through to the semi-finals of the competition five years ago before they were beaten by eventual winners New Zealand.