Build and Runes
Pay attention to how he builds. If he decides to build damage, you can focus him and kill him easily.
Since Udyr has to get into melee range to do anything, taking snares and slows do extremely well against him.
Udyr is weak against mobile champions. Try to pick champions that can kite the udyr.
Always take care of the squishy champions, if Udyr focuses them and your team doesn’t take care of them they’re out completely.