After a reorganization, Grandjean took charge of the 4th Division in the III Corps under Marshal Bon-Adrien Jeannot de Moncey. The division consisted of three battalions of the 5th Light Infantry Regiment, two battalions of the 1st Legion of the Vistula and four battalions of the 2nd Legion of the Reserve. These troops participated in the Battle of Tudela on 23 November 1808, though Grandjean's division did not fire a shot or suffer any casualties. The division was soon broken up and Grandjean assumed command of the 1st Division in the same corps. He led four battalions of the 14th Line, three battalions of the 44th Line, one battalion of the 70th Line and two battalions each of the 2nd and 3rd Legions of the Vistula.