He went on to say: "Look, Hillary Clinton has been doing this most of her life. She is the consummate pro. This is new for Donald, so I think he should over-prepare for it."
Except, all indications are that Trump is not over-preparing for the debate. At all.
The Washington Post reported in August that Trump was not holding any mock debates, instead favoring informal advice sessions over golf and bacon cheeseburgers.
One of Trump's top allies, former New York mayor Rudy Giuliani, said Trump isn't going to be "overscripted" or not himself.
The New York Times reports that he is watching video of Clinton's best and worst debate moments, but his advisers think it's a waste of time to fill his head with facts and statistics. And while Clinton rehearses lines over and over again, Trump doesn't like to.
In what may be Trump's most in-depth debate prep strategy, Politico reported that he hired a team to build a psychological profile of Clinton to try to understand when she feels backed into a corner and take advantage of it. (But at least one Trump adviser called it "wacky pseudo-science.")
Ryan is probably aware of all the ways Trump is (and isn't) preparing for Monday. The House speaker has been on a general election debate stage before, debating Vice President Biden in 2012. And it appears that he thinks that studying your opponent and having informal chats with advisers is not the same as being prepared for a 90-minute face-off on the issues.
A Mitt Romney adviser in 2012, Beth Myers, told me that the campaign started giving Romney briefing books to study in June: "You really have to go onto that stage prepared with a great depth and breadth of knowledge about a lot of topics." (Though she also cautioned against judging anyone's debate prep, saying each candidate is different.)
The contrast between Clinton and Trump's debate prep couldn't be more different. Clinton is poring over similarly thick, detailed briefing books and holding mock debates. On top of that, her aides conducted their own study of Trump's personality to better predict how he might react in given situations, The Post's Abby Philip reports.
In fact, she's arguably the one over-preparing for Monday's debate. She has no choice: She goes into it with more people expecting her to do better than Trump.
At this point, it's probably not a surprise that Ryan thinks Trump should do one thing, while Trump does another. Since Ryan endorsed Trump in June, he has disagreed with the Republican nominee on average every 11 days.
With as many as 100 million people expected to watch Monday's Trump-Clinton showdown, there will be a very public confirmation of whether Trump's decision was the right one, or whether he might have been better off following Ryan's advice after all.