diff --git a/esphome/components/ethernet/__init__.py b/esphome/components/ethernet/__init__.py
index bc26db9956..58915ff96d 100644
--- a/esphome/components/ethernet/__init__.py
+++ b/esphome/components/ethernet/__init__.py
@@ -1,5 +1,4 @@
 from dataclasses import dataclass
-import logging
 
 from esphome import automation, pins
 from esphome.automation import Condition
@@ -62,7 +61,6 @@ from esphome.types import ConfigType
 
 AUTO_LOAD = ["network"]
 DOMAIN = "ethernet"
-LOGGER = logging.getLogger(__name__)
 
 # Key for tracking IP state listener count in CORE.data
 ETHERNET_IP_STATE_LISTENERS_KEY = "ethernet_ip_state_listeners"
@@ -214,13 +212,6 @@ CLK_MODES = {
     "CLK_OUT": emac_rmii_clock_mode_t.EMAC_CLK_OUT,
 }
 
-CLK_MODES_DEPRECATED = {
-    "GPIO0_IN": ("CLK_EXT_IN", 0),
-    "GPIO0_OUT": ("CLK_OUT", 0),
-    "GPIO16_OUT": ("CLK_OUT", 16),
-    "GPIO17_OUT": ("CLK_OUT", 17),
-}
-
 spi_host_device_t = cg.global_ns.enum("spi_host_device_t")
 
 SPI_INTERFACE_MAP = {
@@ -387,23 +378,6 @@ def _validate(config: ConfigType) -> ConfigType:
                 get_esp32_variant,
             )
 
-            if CONF_CLK_MODE in config:
-                mode, pin = CLK_MODES_DEPRECATED[config[CONF_CLK_MODE]]
-                LOGGER.warning(
-                    "[ethernet] The 'clk_mode' option is deprecated. "
-                    "Please replace 'clk_mode: %s' with:\n"
-                    "  clk:\n"
-                    "    mode: %s\n"
-                    "    pin: %s\n"
-                    "Removal scheduled for 2026.11.0.",
-                    config[CONF_CLK_MODE],
-                    mode,
-                    pin,
-                )
-                config[CONF_CLK] = CLK_SCHEMA({CONF_MODE: mode, CONF_PIN: pin})
-                del config[CONF_CLK_MODE]
-            elif CONF_CLK not in config:
-                raise cv.Invalid("'clk' is a required option for [ethernet].")
             variant = get_esp32_variant()
             if variant not in (VARIANT_ESP32, VARIANT_ESP32P4):
                 raise cv.Invalid(
@@ -452,10 +426,17 @@ RMII_SCHEMA = cv.All(
             {
                 cv.Required(CONF_MDC_PIN): pins.internal_gpio_output_pin_number,
                 cv.Required(CONF_MDIO_PIN): pins.internal_gpio_output_pin_number,
-                cv.Optional(CONF_CLK_MODE): cv.enum(
-                    CLK_MODES_DEPRECATED, upper=True, space="_"
+                # Removed in 2026.11.0 - kept to provide helpful error message
+                # Remove before 2027.5.0
+                cv.Optional(CONF_CLK_MODE): cv.invalid(
+                    "The 'clk_mode' option has been removed in ESPHome 2026.11.0.\n"
+                    "Replace it with a 'clk:' block containing 'mode:' and 'pin:':\n"
+                    "  GPIO0_IN   -> mode: CLK_EXT_IN, pin: GPIO0\n"
+                    "  GPIO0_OUT  -> mode: CLK_OUT, pin: GPIO0\n"
+                    "  GPIO16_OUT -> mode: CLK_OUT, pin: GPIO16\n"
+                    "  GPIO17_OUT -> mode: CLK_OUT, pin: GPIO17"
                 ),
-                cv.Optional(CONF_CLK): CLK_SCHEMA,
+                cv.Required(CONF_CLK): CLK_SCHEMA,
                 cv.Optional(CONF_PHY_ADDR, default=0): cv.int_range(min=0, max=31),
                 cv.Optional(CONF_POWER_PIN): pins.internal_gpio_output_pin_number,
                 cv.Optional(CONF_PHY_REGISTERS): cv.ensure_list(PHY_REGISTER_SCHEMA),
diff --git a/tests/benchmarks/python/fixtures/bluetooth_proxy_device.yaml b/tests/benchmarks/python/fixtures/bluetooth_proxy_device.yaml
index dfa5a487b8..c74846689b 100644
--- a/tests/benchmarks/python/fixtures/bluetooth_proxy_device.yaml
+++ b/tests/benchmarks/python/fixtures/bluetooth_proxy_device.yaml
@@ -25,7 +25,9 @@ ethernet:
   type: LAN8720
   mdc_pin: GPIO23
   mdio_pin: GPIO18
-  clk_mode: GPIO17_OUT
+  clk:
+    mode: CLK_OUT
+    pin: GPIO17
   phy_addr: 0
   power_pin: GPIO12
 
diff --git a/tests/component_tests/ethernet/test_ethernet.py b/tests/component_tests/ethernet/test_ethernet.py
index 522357f972..73985597d9 100644
--- a/tests/component_tests/ethernet/test_ethernet.py
+++ b/tests/component_tests/ethernet/test_ethernet.py
@@ -8,6 +8,7 @@ from esphome.components.esp32 import (
     KEY_BOARD,
     KEY_IDF_VERSION,
     KEY_VARIANT,
+    VARIANT_ESP32,
     VARIANT_ESP32S3,
 )
 from esphome.components.ethernet import CONF_CLOCK_SPEED, CONFIG_SCHEMA, _final_validate
@@ -82,3 +83,40 @@ def test_ch390_rejects_clock_speed_above_the_datasheet_maximum(
     CORE.name = "ch390-test"
     with pytest.raises(Invalid, match="value must be at most 72000000"):
         CONFIG_SCHEMA({**_CH390_CONFIG, CONF_CLOCK_SPEED: "80MHz"})
+
+
+_LAN8720_CONFIG = {"type": "LAN8720", "mdc_pin": 23, "mdio_pin": 18}
+
+
+def _set_esp32_core(set_core_config: SetCoreConfigCallable) -> None:
+    set_core_config(
+        PlatformFramework.ESP32_IDF,
+        platform_data={
+            KEY_BOARD: "esp32dev",
+            KEY_VARIANT: VARIANT_ESP32,
+            KEY_IDF_VERSION: cv.Version(5, 3, 2),
+        },
+    )
+    CORE.name = "rmii-test"
+
+
+def test_rmii_rejects_removed_clk_mode(
+    set_core_config: SetCoreConfigCallable,
+) -> None:
+    """The removed clk_mode option points at the clk: replacement."""
+    _set_esp32_core(set_core_config)
+    with pytest.raises(Invalid, match="GPIO17_OUT -> mode: CLK_OUT, pin: GPIO17"):
+        CONFIG_SCHEMA(
+            {
+                **_LAN8720_CONFIG,
+                "clk_mode": "GPIO17_OUT",
+                "clk": {"mode": "CLK_OUT", "pin": 17},
+            }
+        )
+
+
+def test_rmii_requires_clk(set_core_config: SetCoreConfigCallable) -> None:
+    """An RMII PHY has no default clock, so clk must be given."""
+    _set_esp32_core(set_core_config)
+    with pytest.raises(Invalid, match=r"required key not provided @ data\['clk'\]"):
+        CONFIG_SCHEMA(_LAN8720_CONFIG)