If Israel transfers any military equipment to Ukraine that Russia doesnt like, Russia can keep Israel's airforce out of Syria, or even do some attacks on the Israeli army, and US wont be able to protect Israel, simple.
Afterall US wasnt there last year to save ISrael from decapitating and sustained rocket and artillery barrages from the last war against hamas, so US wont be there this time to help ISrael if and when relations with Russia get worse, Russia and Israel are destined to have increasing beef now, because they are firmly in opposite global camps.