Speaking to Sky News, the expert said: “The loss of territory and evacuation of civilians will play poorly back in Russia as evidence they ‘can’t defend themselves’.”
Ukraine has claimed it now controls over 1,000 square metres of Russian territory in the Kursk region a week since the start of the incursion.
However, Mr Savill warned it will be “hard” for Kyiv to maintain a force in Russia because of its “limited reserves.”
He added: “While the Ukrainians have reversed the public narrative about being on the defensive, it seems unlikely they would want to sustain a large incursion for months.
“They will have a decision to make about the best time to trade in the ground they have captured, and to what end.”
The Russian military has so far struggled to deal with the surprise attack, which has led tens of thousands of civilians to flee the region.
For Ukraine, the raid has provided a much-needed boost to morale at a time when its undermanned and under-gunned forces are facing relentless Russian attacks along the more than 1,000-kilometre front line.
Unlike previous raids conducted by small groups of anti-Kremlin Russian volunteers fighting alongside Ukrainian forces, the incursion into the Kursk region reportedly involved units from several battle-hardened Ukrainian army brigades.
Russian military bloggers reported that Ukrainian mobile groups comprised of several armoured vehicles each quickly drove dozens of kilometres into Russian territory, bypassing Russian fortifications and sowing panic throughout the region.
