In January 1917 Rosetti was put in command of the 55th/67th Infantry Regiment, with troops from Piatra Neamț and Bacău, and garrisoned at Vorniceni, near Botoșani. In April he fell ill with typhus, and was moved to the Charity Hospital in Iași, where he stayed until May. At the request of General Constantin Prezan, Rosetti took command on 4 June of the 4th/72nd Infantry Regiment, composed of units from Ploiești and Mizil. With this regiment he fought fiercely at the Battle of Mărășești, under the command of General Eremia Grigorescu. On 19 August he was badly wounded by machine gun fire at Răzoare. He was then transported to the French Hospital of Notre Dame de Sion in Iași, where he was treated by Dr. E. Sorrel, and was visited by Ion I. C. Brătianu, Barbu Știrbei, and the Royal Family. For his bravery on the battlefield, Rosetti was awarded on 9 October the Order of Michael the Brave, third class.