diff --git a/dd-java-agent/instrumentation/java-concurrent/java-concurrent-21/build.gradle b/dd-java-agent/instrumentation/java-concurrent/java-concurrent-21/build.gradle
index 361477f06ff..6c1b1ff4afc 100644
--- a/dd-java-agent/instrumentation/java-concurrent/java-concurrent-21/build.gradle
+++ b/dd-java-agent/instrumentation/java-concurrent/java-concurrent-21/build.gradle
@@ -6,6 +6,8 @@ ext {
 }
 
 apply from: "$rootDir/gradle/java.gradle"
+// Use slf4j-simple as default; logback has a high chance of getting stuck in a deadlock on CI.
+apply from: "$rootDir/gradle/slf4j-simple.gradle"
 apply plugin: 'idea'
 
 muzzle {
diff --git a/dd-java-agent/instrumentation/java-concurrent/java-concurrent-21/src/test/groovy/VirtualThreadTest.groovy b/dd-java-agent/instrumentation/java-concurrent/java-concurrent-21/src/test/groovy/VirtualThreadTest.groovy
index ccd652dfc81..9ace7d7f467 100644
--- a/dd-java-agent/instrumentation/java-concurrent/java-concurrent-21/src/test/groovy/VirtualThreadTest.groovy
+++ b/dd-java-agent/instrumentation/java-concurrent/java-concurrent-21/src/test/groovy/VirtualThreadTest.groovy
@@ -59,17 +59,15 @@ class VirtualThreadTest extends AgentTestRunner {
     }
 
     where:
-    // spotless:off
-    name                     | method              | poolImpl
-    "execute Runnable"       | executeRunnable     | Executors.newVirtualThreadPerTaskExecutor()
-    "submit Runnable"        | submitRunnable      | Executors.newVirtualThreadPerTaskExecutor()
-    "submit Callable"        | submitCallable      | Executors.newVirtualThreadPerTaskExecutor()
+    name                     | method                                  | poolImpl
+    "execute Runnable"       | executeRunnable                         | Executors.newVirtualThreadPerTaskExecutor()
+    "submit Runnable"        | submitRunnable                          | Executors.newVirtualThreadPerTaskExecutor()
+    "submit Callable"        | submitCallable                          | Executors.newVirtualThreadPerTaskExecutor()
     "submit Runnable ECS"    | submitRunnableExecutorCompletionService | new ExecutorCompletionService<>(Executors.newVirtualThreadPerTaskExecutor())
-    "submit Callable ECS"    | submitCallable      | new ExecutorCompletionService<>(Executors.newVirtualThreadPerTaskExecutor())
-    "invokeAll"              | invokeAll           | Executors.newVirtualThreadPerTaskExecutor()
-    "invokeAll with timeout" | invokeAllTimeout    | Executors.newVirtualThreadPerTaskExecutor()
-    "invokeAny"              | invokeAny           | Executors.newVirtualThreadPerTaskExecutor()
-    "invokeAny with timeout" | invokeAnyTimeout    | Executors.newVirtualThreadPerTaskExecutor()
-     // spotless:on
+    "submit Callable ECS"    | submitCallable                          | new ExecutorCompletionService<>(Executors.newVirtualThreadPerTaskExecutor())
+    "invokeAll"              | invokeAll                               | Executors.newVirtualThreadPerTaskExecutor()
+    "invokeAll with timeout" | invokeAllTimeout                        | Executors.newVirtualThreadPerTaskExecutor()
+    "invokeAny"              | invokeAny                               | Executors.newVirtualThreadPerTaskExecutor()
+    "invokeAny with timeout" | invokeAnyTimeout                        | Executors.newVirtualThreadPerTaskExecutor()
   }
 }
diff --git a/dd-java-agent/testing/src/main/groovy/datadog/trace/agent/test/AgentTestRunner.groovy b/dd-java-agent/testing/src/main/groovy/datadog/trace/agent/test/AgentTestRunner.groovy
index 8c70e25d876..20fe0333b4d 100644
--- a/dd-java-agent/testing/src/main/groovy/datadog/trace/agent/test/AgentTestRunner.groovy
+++ b/dd-java-agent/testing/src/main/groovy/datadog/trace/agent/test/AgentTestRunner.groovy
@@ -1,7 +1,6 @@
 package datadog.trace.agent.test
 
 import ch.qos.logback.classic.Level
-import ch.qos.logback.classic.Logger
 import ch.qos.logback.classic.util.ContextInitializer
 import com.datadog.debugger.agent.ClassesToRetransformFinder
 import com.datadog.debugger.agent.Configuration
@@ -68,6 +67,7 @@ import net.bytebuddy.utility.JavaModule
 import okhttp3.HttpUrl
 import okhttp3.OkHttpClient
 import org.junit.runner.RunWith
+import org.slf4j.Logger
 import org.slf4j.LoggerFactory
 import org.spockframework.mock.MockUtil
 import org.spockframework.mock.runtime.MockInvocation
@@ -289,12 +289,16 @@ abstract class AgentTestRunner extends DDSpecification implements AgentBuilder.L
     true
   }
 
+  @SuppressForbidden
   private static void configureLoggingLevels() {
     def logger = LoggerFactory.getLogger(Logger.ROOT_LOGGER_NAME)
-    if (!(logger instanceof Logger)) {
+
+    // Check logger class by name to avoid NoClassDefFoundError at runtime for tests without Logback.
+    if (logger.class.name != "ch.qos.logback.classic.Logger") {
       return
     }
-    final Logger rootLogger = logger
+
+    final ch.qos.logback.classic.Logger rootLogger = (ch.qos.logback.classic.Logger)logger
     if (!rootLogger.iteratorForAppenders().hasNext()) {
       try {
         // previous test wiped out the logging config bring it back for the next test
@@ -305,11 +309,10 @@ abstract class AgentTestRunner extends DDSpecification implements AgentBuilder.L
     }
 
     rootLogger.setLevel(Level.WARN)
-    ((Logger) LoggerFactory.getLogger("datadog")).setLevel(Level.DEBUG)
-    ((Logger) LoggerFactory.getLogger("org.testcontainers")).setLevel(Level.DEBUG)
+    ((ch.qos.logback.classic.Logger) LoggerFactory.getLogger("datadog")).setLevel(Level.DEBUG)
+    ((ch.qos.logback.classic.Logger) LoggerFactory.getLogger("org.testcontainers")).setLevel(Level.DEBUG)
   }
 
-
   def codeOriginSetup() {
     injectSysConfig(CODE_ORIGIN_FOR_SPANS_ENABLED, "true", true)
     injectSysConfig(DYNAMIC_INSTRUMENTATION_VERIFY_BYTECODE, "false", true)
diff --git a/gradle/slf4j-simple.gradle b/gradle/slf4j-simple.gradle
new file mode 100644
index 00000000000..a83ef57a71a
--- /dev/null
+++ b/gradle/slf4j-simple.gradle
@@ -0,0 +1,27 @@
+// Apply this script when `slf4j-simple` should be used instead of `logback`.
+
+configurations.configureEach { cfg ->
+  def name = cfg.name
+
+  if (name.containsIgnoreCase("test")) {
+    // Exclude Logback from all test-like runtimeClasspath configurations.
+    if (name.endsWithIgnoreCase("runtimeClasspath")) {
+      cfg.exclude group: "ch.qos.logback"
+    }
+
+    // Add slf4j-simple to all test-like runtimeOnly configurations.
+    if (name.endsWithIgnoreCase("runtimeOnly")) {
+      project.dependencies.add(name, "org.slf4j:slf4j-simple:${libs.versions.slf4j.get()}")
+    }
+  }
+}
+
+// Configure `slf4j-simple` logger.
+tasks.withType(Test).configureEach {
+  jvmArgs += [
+    "-Dorg.slf4j.simpleLogger.defaultLogLevel=debug",
+    "-Dorg.slf4j.simpleLogger.showThreadName=true",
+    "-Dorg.slf4j.simpleLogger.showDateTime=true",
+    "-Dorg.slf4j.simpleLogger.dateTimeFormat=HH:mm:ss.SSS"
+  ]
+}