Actually, I think He did.
God gave warnings of false teaching through His prophets.
And the word of the Lord came to me, saying, “Son of man, prophesy against the prophets of Israel who prophesy, and say to those who prophesy out of their own heart, ‘Hear the word of the Lord!’ ” Thus says the Lord God: “Woe to the foolish prophets, who follow their own spirit and have seen nothing! O Israel, your prophets are like foxes in the deserts. You have not gone up into the gaps to build a wall for the house of Israel to stand in battle on the day of the Lord. They have envisioned futility and false divination, saying, ‘Thus says the Lord!’ But the Lord has not sent them; yet they hope that the word may be confirmed. Have you not seen a futile vision, and have you not spoken false divination? You say, ‘The Lord says,’ but I have not spoken.” Therefore thus says the Lord God: “Because you have spoken nonsense and envisioned lies, therefore I am indeed against you,” says the Lord God. “My hand will be against the prophets who envision futility and who divine lies; they shall not be in the assembly of My people, nor be written in the record of the house of Israel, nor shall they enter into the land of Israel. Then you shall know that I am the Lord God.
Ezekiel 13:1-9 NKJV
And the Lord said to me, “The prophets prophesy lies in My name. I have not sent them, commanded them, nor spoken to them; they prophesy to you a false vision, divination, a worthless thing, and the deceit of their heart. Therefore thus says the Lord concerning the prophets who prophesy in My name, whom I did not send, and who say, ‘Sword and famine shall not be in this land’—‘By sword and famine those prophets shall be consumed!"
Jeremiah 14:14-15 NKJV
Jesus warned of false teachings.
"Beware of false prophets, who come to you in sheep's clothing, but inwardly they are ravenous wolves. You will know them by their fruits. Do men gather grapes from thornbushes or figs from thistles? Even so, every good tree bears good fruit, but a bad tree bears bad fruit. A good tree cannot bear bad fruit, nor can a bad tree bear good fruit. Every tree that does not bear good fruit is cut down and thrown into the fire. Therefore by their fruits you will know them."
Matthew 7:15-20 NKJV
"There will be great tribulation, such as has not been since the beginning of the world until this time, no, nor ever shall be. And unless those days were shortened, no flesh would be saved; but for the elect's sake those days will be shortened. Then if anyone says to you, 'Look, here is the Christ!' or 'There!' do not believe it. For false christs and false prophets will rise and show great signs and wonders to deceive, if possible, even the elect."
Matthew 24:21-24 NKJV
Paul too gave warnings.
For the time will come when they will not endure sound doctrine, but according to their own desires, because they have itching ears, they will heap up for themselves teachers; and they will turn their ears away from the truth, and be turned aside to fables.
2 Timothy 4:3-4 NKJV
Peter gave warnings as well.
Therefore, beloved, looking forward to these things, be diligent to be found by Him in peace, without spot and blameless; and consider that the longsuffering of our Lord is salvation—as also our beloved brother Paul, according to the wisdom given to him, has written to you, as also in all his epistles, speaking in them of these things, in which are some things hard to understand, which untaught and unstable people twist to their own destruction, as they do also the rest of the Scriptures. You therefore, beloved, since you know this beforehand, beware lest you also fall from your own steadfastness, being led away with the error of the wicked; but grow in the grace and knowledge of our Lord and Savior Jesus Christ.
2 Peter 3:14-18 NKJV