diff --git a/monai/data/image_reader.py b/monai/data/image_reader.py
index 16e8514f48..39fc1f46b4 100644
--- a/monai/data/image_reader.py
+++ b/monai/data/image_reader.py
@@ -639,7 +639,7 @@ class WSIReader(ImageReader):
 
     """
 
-    def __init__(self, reader_lib: str = "cuClaraImage"):
+    def __init__(self, reader_lib: str = "OpenSlide"):
         super().__init__()
         self.reader_lib = reader_lib.lower()
         if self.reader_lib == "openslide":
@@ -672,6 +672,11 @@ def read(self, data: Union[Sequence[str], str, np.ndarray], **kwargs):
             data: file name or a list of file names to read.
 
         """
+        if (self.reader_lib == "openslide") and (not has_osl):
+            raise ImportError("No module named 'openslide'")
+        elif (self.reader_lib == "cuclaraimage") and (not has_cux):
+            raise ImportError("No module named 'cuimage'")
+
         img_: List = []
 
         filenames: Sequence[str] = ensure_tuple(data)