The Hoops saw their hopes of reaching the last 16 of the competition ended with a 3-0 defeat to AC Milan on Tuesday evening.
Vennegoor of Hesselink believes that the club have not found an adequate replacement for striker Hooper, who was sold to Norwich City during the summer.
"There are good players in that squad but they lost some important ones during the summer," he told Sky Sports News.
"If you look at the squad and the resources Neil Lennon has, he did a good job by qualifying for the Champions League group stages, but you can always use a fresh injection of players into your squad.
"They could do with a goalscorer like Gary Hooper. I don't know if Celtic are on the lookout for a striker but from looking at the Milan game, they need an out-and-out goalscorer."
Vennegoor of Hesselink played for Celtic between 2006 and 2009.