Keane slammed the Dane after United's defeat at Chelsea on Friday night.
"They have got no striker," Keane said on Sky Sports. "Hojlund tonight, he looked like the young kid from Chelsea (Tyrique George).
"He looked like he had just come out of the academy. His runs weren't right, his timing, his hold-up play. Again, if you're a striker playing for Man United... even for the whole team, one shot on target?"
Keane also said: "We keep making excuses for him. We talk about confidence, but you still think, when you're a striker, you have to make something happen sometimes.
"What the big clubs have - and what United have always had - is strikers who can produce something for themselves even if they're not getting great service. They produce something because they have quality, a bit of determination, a bit of experience, football intelligence. We don't see that with Hojlund.
"His side are up against it all the time. Obviously he needs a little bit of support, but, my goodness, sometimes you have just got to do a little bit better."