diff --git a/changelog.d/3091.misc.rst b/changelog.d/3091.misc.rst
new file mode 100644
index 0000000000..d66641253a
--- /dev/null
+++ b/changelog.d/3091.misc.rst
@@ -0,0 +1,4 @@
+Make ``concurrent.futures`` import lazy in vendored ``more_itertools``
+package to a  avoid importing threading as a side effect (which caused
+`gevent/gevent#1865 <https://github.com/gevent/gevent/issues/1865>`__).
+-- by :user:`maciejp-ro`
diff --git a/pkg_resources/_vendor/more_itertools/more.py b/pkg_resources/_vendor/more_itertools/more.py
index 630af973f2..6b6a5cab25 100644
--- a/pkg_resources/_vendor/more_itertools/more.py
+++ b/pkg_resources/_vendor/more_itertools/more.py
@@ -2,7 +2,6 @@
 
 from collections import Counter, defaultdict, deque, abc
 from collections.abc import Sequence
-from concurrent.futures import ThreadPoolExecutor
 from functools import partial, reduce, wraps
 from heapq import merge, heapify, heapreplace, heappop
 from itertools import (
@@ -3656,7 +3655,7 @@ def __init__(self, func, callback_kwd='callback', wait_seconds=0.1):
         self._aborted = False
         self._future = None
         self._wait_seconds = wait_seconds
-        self._executor = ThreadPoolExecutor(max_workers=1)
+        self._executor = __import__("concurrent.futures").futures.ThreadPoolExecutor(max_workers=1)
         self._iterator = self._reader()
 
     def __enter__(self):
diff --git a/setuptools/_vendor/more_itertools/more.py b/setuptools/_vendor/more_itertools/more.py
index 0f7d282aa5..e6fca4d47f 100644
--- a/setuptools/_vendor/more_itertools/more.py
+++ b/setuptools/_vendor/more_itertools/more.py
@@ -2,7 +2,6 @@
 
 from collections import Counter, defaultdict, deque, abc
 from collections.abc import Sequence
-from concurrent.futures import ThreadPoolExecutor
 from functools import partial, reduce, wraps
 from heapq import merge, heapify, heapreplace, heappop
 from itertools import (
@@ -3454,7 +3453,7 @@ def __init__(self, func, callback_kwd='callback', wait_seconds=0.1):
         self._aborted = False
         self._future = None
         self._wait_seconds = wait_seconds
-        self._executor = ThreadPoolExecutor(max_workers=1)
+        self._executor = __import__("concurrent.futures").futures.ThreadPoolExecutor(max_workers=1)
         self._iterator = self._reader()
 
     def __enter__(self):
diff --git a/tools/vendored.py b/tools/vendored.py
index 57e28d53c4..ee978e5c82 100644
--- a/tools/vendored.py
+++ b/tools/vendored.py
@@ -64,6 +64,21 @@ def rewrite_importlib_resources(pkg_files, new_root):
         file.write_text(text)
 
 
+def rewrite_more_itertools(pkg_files: Path):
+    """
+    Defer import of concurrent.futures. Workaround for #3090.
+    """
+    more_file = pkg_files.joinpath('more.py')
+    text = more_file.read_text()
+    text = re.sub(r'^.*concurrent.futures.*?\n', '', text, flags=re.MULTILINE)
+    text = re.sub(
+        'ThreadPoolExecutor',
+        '__import__("concurrent.futures").futures.ThreadPoolExecutor',
+        text,
+    )
+    more_file.write_text(text)
+
+
 def clean(vendor):
     """
     Remove all files out of the vendor directory except the meta
@@ -96,6 +111,7 @@ def update_pkg_resources():
     rewrite_jaraco_text(vendor / 'jaraco/text', 'pkg_resources.extern')
     rewrite_jaraco(vendor / 'jaraco', 'pkg_resources.extern')
     rewrite_importlib_resources(vendor / 'importlib_resources', 'pkg_resources.extern')
+    rewrite_more_itertools(vendor / "more_itertools")
 
 
 def update_setuptools():
@@ -105,6 +121,7 @@ def update_setuptools():
     rewrite_jaraco_text(vendor / 'jaraco/text', 'setuptools.extern')
     rewrite_jaraco(vendor / 'jaraco', 'setuptools.extern')
     rewrite_importlib_resources(vendor / 'importlib_resources', 'setuptools.extern')
+    rewrite_more_itertools(vendor / "more_itertools")
 
 
 __name__ == '__main__' and update_vendored()