He took part in the preparation for a war against Muscovy in 1579–1581, where he contributed a group of 400 or 600 mercenaries. Through he had little prior military background nor experience, he was interested in mastering the military art, and proved to be an adept learner. With Batory's support, he began filling in for some of the roles of Grand Crown Hetman Mikołaj Mielecki, particularly when Mielecki was not present. While not campaigning, he was also instrumental in ensuring that the ongoing political support for the war. In 1580 he was hit by another personal tragedy, as his wife died in labor, together with their child; entering a short period of depression.