The American said the financial outlay on the group of players in terms of salaries was huge in comparison to the resources available.
FSG paid £300million to buy the club from Tom Hicks and George Gillett in October but Henry admitted tackling problems with the squad was "a bigger issue than we feared".
"The worst surprise was the lack of depth in the squad," the American told FourFourTwo magazine.
"Our biggest concern in taking on this responsibility was this issue and it was a bigger issue than we feared.
"There was a huge multi-year pay-roll for a squad that had very little depth."
Source: PA