Ex-Celtic striker Jan Vennegoor of Hesselink says the club must seek to replace Gary Hooper if they're to prevent further failures after Neil Lennon's side were dumped out of Europe following defeat to AC Milan.
Ajax's surprise win over Barcelona sees the Bhoys crash out of the Champions League group phase, while the Scottish Premiership champions will also miss out on dropping into the Europa League.
Celtic could only muster one win and two goals from their five group matches so far, and a lacklustre 3-0 loss to Milan exposed their problems in front of goal - issues that have been heightened since the summer sale of Hooper to Norwich City.
The Englishman netted 29 goals in 43 starts in his final campaign with the Hoops and Vennegoor of Hesselink has urged the club to invest in a replacement.
"There are good players in that squad but they lost some important ones during the summer," the Dutchman said.
"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."
Celtic's finances are often hamstrung by the lack of rewards in Scottish football meaning investment in players in slow in coming despite the summer signings of Temmu Pukki and Virgil van Dijk.
Vennegoor of Hesselink says it is important the club bounce back domestically.
"Everyone expected more, especially before the Milan game," he added.
"They thought they could reach the last-16 or the knockout stages of the Europa League, but with one game left to play their campaign is already over.
"They now need to pick themselves up and try and win the league and cup. They're a young squad and hopefully they can learn from their mistakes."