With the under-17 team, Grenier was a regular and scored on his debut in a 4–0 victory over Switzerland. Grenier scored a hat trick in the team's 6–0 thrashing of Albania in the first qualifying round of the 2008 UEFA European Under-17 Championship. At the Algarve Cup in Portugal, he helped the team to second place by scoring a brace in the team's 4–2 win against Denmark. Grenier scored his only goal against Israel in a second group stage match. France finished the round unbeaten and qualified for the tournament. During the Championship, Grenier scored in a 3–3 draw with Spain, converting on a curling free-kick in the 43rd minute. France later reached the final where they were defeated 4–0 by Spain.