diff --git a/src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/checks/GameLobbyExistsCheck.java b/src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/checks/GameLobbyExistsCheck.java
new file mode 100644
index 0000000..fba5240
--- /dev/null
+++ b/src/main/java/ch/unibas/dmi/dbis/cs108/casono/server/app/checks/GameLobbyExistsCheck.java
@@ -0,0 +1,75 @@
+package ch.unibas.dmi.dbis.cs108.casono.server.app.checks;
+
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.game.bet.PlayerBetRequest;
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.game.call.PlayerCallRequest;
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.game.fold.PlayerFoldRequest;
+import ch.unibas.dmi.dbis.cs108.casono.server.app.commands.game.raise.PlayerRaiseRequest;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.lobby.Lobby;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.lobby.LobbyId;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.lobby.LobbyManager;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.user.User;
+import ch.unibas.dmi.dbis.cs108.casono.server.domain.user.UserRegistry;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.command.execution.checks.HandlerCheck;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.request.Request;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.ErrorResponse;
+import ch.unibas.dmi.dbis.cs108.casono.server.network.protocol.response.Response;
+import java.util.Optional;
+
+/**
+ * Checks whether a target lobby exists for game action commands.
+ *
+ * <p>Supported commands are BET, CALL, FOLD and RAISE. If a request specifies a GAME_ID, the check
+ * validates that this lobby exists. Otherwise, it validates that the logged-in user is in a lobby.
+ */
+public class GameLobbyExistsCheck implements HandlerCheck {
+    private final UserRegistry userRegistry;
+    private final LobbyManager lobbyManager;
+
+    public GameLobbyExistsCheck(UserRegistry userRegistry, LobbyManager lobbyManager) {
+        this.userRegistry = userRegistry;
+        this.lobbyManager = lobbyManager;
+    }
+
+    @Override
+    public Optional<Response> check(Request request) {
+        Integer gameId = extractGameId(request);
+        User user = userRegistry.getBySessionId(request.getSessionId()).get();
+
+        Lobby lobby;
+        if (gameId != null) {
+            lobby = lobbyManager.getLobby(LobbyId.of(gameId));
+        } else {
+            lobby = lobbyManager.getLobbyByUsername(user.getName());
+        }
+
+        if (lobby != null) {
+            return Optional.empty();
+        }
+
+        if (gameId != null) {
+            return Optional.of(
+                    new ErrorResponse(request.getContext(), "LOBBY_NOT_FOUND", "Lobby not found"));
+        }
+
+        return Optional.of(
+                new ErrorResponse(request.getContext(), "NOT_IN_LOBBY", "User not in a lobby"));
+    }
+
+    private Integer extractGameId(Request request) {
+        if (request instanceof PlayerBetRequest) {
+            return ((PlayerBetRequest) request).getGameId();
+        }
+        if (request instanceof PlayerCallRequest) {
+            return ((PlayerCallRequest) request).getGameId();
+        }
+        if (request instanceof PlayerFoldRequest) {
+            return ((PlayerFoldRequest) request).getGameId();
+        }
+        if (request instanceof PlayerRaiseRequest) {
+            return ((PlayerRaiseRequest) request).getGameId();
+        }
+
+        throw new IllegalStateException(
+                "GameLobbyExistsCheck is only supported for BET, CALL, FOLD and RAISE requests");
+    }
+}