Henry believes a disappointing 0-0 draw with Aston Villa was the turning point in Newcastle's relegation from the Premier League.
The Magpies were the only team in the top division that failed to beat Eric Black's men over the past season, and saw their second relegation in seven years confirmed following Sunderland's 3-0 win over Everton last Wednesday.
Despite an impressive 5-1 win over Tottenham on the last day, attention on Tyneside will now turn to preparing a successful promotion charge from the Championship, with current boss Rafael Benitez reportedly edging closer to committing his long-term future to the club.
But inquests into what went wrong will have already begun at St James' Park, with Henry under no doubt that the players bought by the club during an extravagant transfer window were not of the calibre required to propel them away from danger, adding that an inability to beat Villa was testament to the squad's failings.
According to Squawka, he told Sky Sports: "Sunderland bought players who straight away had an impact on the team. When you look at the players that went to Newcastle: Jonjo Shelvey started well in his first game; Townsend you could say maybe finished well but Henri Saivet wasn’t there, and Seydou Doumbia made a couple of appearances.
“One thing that sums it up for me, if you don’t win at Villa and you need to stay up you don’t deserve to stay up, I’m sorry. That’s as simple as that."