diff --git a/spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/server/WebTestClientContextCustomizerFactory.java b/spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/server/WebTestClientContextCustomizerFactory.java
index 8582af1bb3e5..e41fab860895 100644
--- a/spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/server/WebTestClientContextCustomizerFactory.java
+++ b/spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/web/reactive/server/WebTestClientContextCustomizerFactory.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2021 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -29,21 +29,36 @@
  * {@link ContextCustomizerFactory} for {@code WebTestClient}.
  *
  * @author Stephane Nicoll
+ * @author Andy Wilkinson
  */
 class WebTestClientContextCustomizerFactory implements ContextCustomizerFactory {
 
-	private static final String WEB_TEST_CLIENT_CLASS = "org.springframework.web.reactive.function.client.WebClient";
+	private static final boolean reactorClientPresent;
+
+	private static final boolean jettyClientPresent;
+
+	private static final boolean httpComponentsClientPresent;
+
+	private static final boolean webClientPresent;
+
+	static {
+		ClassLoader loader = WebTestClientContextCustomizerFactory.class.getClassLoader();
+		reactorClientPresent = ClassUtils.isPresent("reactor.netty.http.client.HttpClient", loader);
+		jettyClientPresent = ClassUtils.isPresent("org.eclipse.jetty.client.HttpClient", loader);
+		httpComponentsClientPresent = ClassUtils
+				.isPresent("org.apache.hc.client5.http.impl.async.CloseableHttpAsyncClient", loader)
+				&& ClassUtils.isPresent("org.apache.hc.core5.reactive.ReactiveDataConsumer", loader);
+		webClientPresent = ClassUtils.isPresent("org.springframework.web.reactive.function.client.WebClient", loader);
+	}
 
 	@Override
 	public ContextCustomizer createContextCustomizer(Class<?> testClass,
 			List<ContextConfigurationAttributes> configAttributes) {
 		SpringBootTest springBootTest = TestContextAnnotationUtils.findMergedAnnotation(testClass,
 				SpringBootTest.class);
-		return (springBootTest != null && isWebClientPresent()) ? new WebTestClientContextCustomizer() : null;
-	}
-
-	private boolean isWebClientPresent() {
-		return ClassUtils.isPresent(WEB_TEST_CLIENT_CLASS, getClass().getClassLoader());
+		return (springBootTest != null && webClientPresent
+				&& (reactorClientPresent || jettyClientPresent || httpComponentsClientPresent))
+						? new WebTestClientContextCustomizer() : null;
 	}
 
 }
diff --git a/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/web/reactive/server/WebTestClientContextCustomizerWithoutSupportedHttpClientTests.java b/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/web/reactive/server/WebTestClientContextCustomizerWithoutSupportedHttpClientTests.java
new file mode 100644
index 000000000000..2a83f992ce13
--- /dev/null
+++ b/spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/web/reactive/server/WebTestClientContextCustomizerWithoutSupportedHttpClientTests.java
@@ -0,0 +1,51 @@
+/*
+ * Copyright 2012-2021 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.test.web.reactive.server;
+
+import java.util.Collections;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.boot.test.context.SpringBootTest;
+import org.springframework.boot.testsupport.classpath.ClassPathExclusions;
+import org.springframework.test.context.ContextCustomizer;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link WebTestClientContextCustomizerFactory} when no supported HTTP client
+ * is on the classpath.
+ *
+ * @author Andy Wilkinson
+ */
+@ClassPathExclusions({ "reactor-netty*.jar", "jetty-client*.jar" })
+public class WebTestClientContextCustomizerWithoutSupportedHttpClientTests {
+
+	@Test
+	void createContextCustomizerWhenNoSupportedHttpClientIsAvailableShouldReturnNull() {
+		WebTestClientContextCustomizerFactory contextCustomizerFactory = new WebTestClientContextCustomizerFactory();
+		ContextCustomizer contextCustomizer = contextCustomizerFactory.createContextCustomizer(TestClass.class,
+				Collections.emptyList());
+		assertThat(contextCustomizer).isNull();
+	}
+
+	@SpringBootTest(webEnvironment = SpringBootTest.WebEnvironment.RANDOM_PORT)
+	private static class TestClass {
+
+	}
+
+}