diff --git a/scrapy/extensions/throttle.py b/scrapy/extensions/throttle.py
index cdb0671ae..e98af05b1 100644
--- a/scrapy/extensions/throttle.py
+++ b/scrapy/extensions/throttle.py
@@ -45,18 +45,17 @@ class AutoThrottle:
     def _spider_opened(self, spider: Spider) -> None:
         self.mindelay = self._min_delay(spider)
         self.maxdelay = self._max_delay(spider)
-        spider.download_delay = self._start_delay(spider)  # type: ignore[attr-defined]
 
     def _min_delay(self, spider: Spider) -> float:
-        s = self.crawler.settings
-        return getattr(spider, "download_delay", s.getfloat("DOWNLOAD_DELAY"))
+        return self.crawler.settings.getfloat("DOWNLOAD_DELAY")
 
     def _max_delay(self, spider: Spider) -> float:
         return self.crawler.settings.getfloat("AUTOTHROTTLE_MAX_DELAY")
 
     def _start_delay(self, spider: Spider) -> float:
         return max(
-            self.mindelay, self.crawler.settings.getfloat("AUTOTHROTTLE_START_DELAY")
+            self.crawler.settings.getfloat("DOWNLOAD_DELAY"),
+            self.crawler.settings.getfloat("AUTOTHROTTLE_START_DELAY"),
         )
 
     def _response_downloaded(