The Russian forces at Nasielsk consisted of the rearguard that was covering the retreat from Czarnowo and the main body under the direct command of Ostermann-Tolstoi. Details concerning the composition of both rearguard and main body are lacking. The rearguard is identified as three battalions of jäger, probably 20th Jäger, and two battalions of the Pavlov Grenadiers, supported by some artillery and 3-5 squadrons of Alexandria Hussars. Based on the roads and probable route of retreat, it is safe to conclude that the main body was composed of all remaining forces from the Czarnowo-Izbice-Nasielsk triangle. This would include Rostov and Yelets Musketeers, St. Petersburg Grenadiers, two additional battalions of jäger, Kargopol Dragoons and perhaps also Leib Cuirassiers. The bulk of the artillery of 2nd division would also have been present, less the artillery assigned to the rearguard and the guns captured by the French at Czarnowo. Based on marching times of other units, the forces retiring from the Narew would have begun to extricate themselves after 4:00 AM, with the first elements arriving at Nasielsk by around 8:00 AM. We can conclude that the forces at Debe would have left somewhat later, perhaps as late as daybreak (around 8:00 AM) and arrived by 11:00 AM at the latest. Thus the entire force would have been concentrated at Nasielsk before Kaminski’s arrival.
Around noon on 24 December, FM Kamensky arrived at Nasielsk. Surveying the situation, Kamensky determined to concentrate his forces at Strzegoczin. This decision was made by around 12:30, and the main body of Ostermann’s forces, still covered by a rearguard, began to withdraw northward shortly thereafter. French reports do not mention the withdrawal of the Russian main body, indicating that the woods north of Nasielsk and the Russian cavalry effectively screened this withdrawal. The composition of the Russian rearguard covering the withdrawal is not clear, but it is safe to conclude that it was comprised of 3-5 battalions of jäger and several additional battalions of musketeers or grenadiers along with Alexandria Hussars (probably 10 squadrons) and perhaps a regiment of Cossacks – in total up to 8 battalions and 10 squadrons with ?? guns, or in the neighborhood of 5,000 men.
Rapp and Lemarois arrived around noon with their cavalry. Friant's 1st brigade (Lochet) had reached a point about 1 km south of Nasielsk around 1:30 PM. It seems likely that Ostermann's main body was clear of Nasielsk before the French attacked.
Dorochow arrived from Borkowo late in the action, but it seems he only had his cavalry with him (5 squadrons Isoum and possibly cossacks), no mention of Jager which may have retired towards Nowemiasto from Borkowo (makes sense as the jager were part of Barclay's command and that was where Barclay had fallen back to while Dorochow was assigned to 2nd division).