Former Celtic players Charlie Nicolas and Andy Walker accused the club of refusing to invest sufficiently in the squad after the Scottish champions wasted a Champions League reprieve by crashing out of the competition in the play-off round.
Having been beaten 6-1 on aggregate by Legia Warsaw in the previous qualifying round, Celtic were reinstated in the tournament by UEFA because the Polish club had fielded a suspended player for the last few minutes of the second leg.
However, after drawing 1-1 away at Slovenian champions NK Maribor last week, they lost Tuesday's home match 1-0 and will now play in the Europa League instead of the highly lucrative Champions League group stages.
Rubbing salt into the wounds of elimination is the fact that Norwegian manager Ronny Deila and his team have achieved the unwanted distinction of being knocked out of the same competition twice in three weeks.
"I think they're stockpiling cash," former Scottish international winger Andy Walker, who played almost 200 times for the club, told Sky Sports on Wednesday.
"They're not prepared to pay serious money for anyone with pedigree. They're very much a selling club."
Former hero Charlie Nicholas was equally critical, claiming of the 45-time Scottish champions and 1967 European Cup winners: "The only interest of board members is cash and finance. That's why they spend £2million on budget players who don't have any experience of the Champions League.
"The quality they've brought in is very, very poor. In the cold light of day what's going to happen is that fans won't be turning up and Celtic can write off the trust that the fans were giving them."
Terry Butcher, the former England international who played for great rivals Rangers, added: "They're not even half the side they were. It's really disappointing for Scottish football."
Meanwhile, Celtic have completed the loan signing of Ghana winger Mubarak Wakaso.
The 24-year-old, who played in the World Cup, arrives on a one-year loan deal with Celtic having the option to buy the player from Russian side Rubin Kazan.
Celtic announced the former Espanyol and Villarreal player will go straight into their squad for Sunday's Scottish Premiership clash at Dundee.