Putin's possible responses:

I think the first one mentioned is the most likely.

https://nationalinterest.org/feature/west-won’t-russia’s-next-move-ukraine-204873

Option 1: Moscow could launch a counter-counteroffensive—one focused on the Black Sea port of Odessa. That city is Ukraine’s last outlet on the Black Sea, and its seizure would effectively make Ukraine a landlocked country. It would also give Russia a stranglehold on Ukraine’s principal economic lifeline, since the majority of Kyiv’s exports and imports flow through Odessa. The loss of that city would be a colossal economic and psychological blow to Ukraine. Given that Russia redeployed sizable numbers of troops and quantities of weapons from eastern Ukraine to the south even before Kyiv’s eastern offensive, there is a high probability that Odessa is now Moscow’s principal target. Already overextended Ukrainian forces in the south would be very hard-pressed to repel a concerted Russian attack.