Dietmar Hamann has warned Liverpool's owners to get things right this summer, or face a decade away from the Champions League.
Liverpool endured a dreadful league campaign under Kenny Dalglish, finishing eighth behind neighbours Everton. The Reds' 2011-12 performance represents their worst finish for nearly 20 years.
The future of boss Dalglish is currently under much scrutiny, following a brief trip to Boston to speak to the club's American owners. Widespread reports claim Dalglish has been asked to "move upstairs" at Anfield, and an official announcement on the Scot's future is expected later this week.
Hamann prefers not to focus specifically on Dalglish, insisting whoever is in charge must make the right moves in the transfer market - regardless of budget - or face leading the Reds into an era of mediocrity.
"It's a worrying time for Liverpool - the most important summer for them," the 2005 Champions League winner said in the Daily Mirror.
"If they don't make the right decisions, we may not see Champions League football at Anfield for the next five or 10 years, which is a very likely scenario at the moment.
"The owners need to make a decision whether he [Dalglish] is the man to take the club forward. The improvement has to come from somewhere because, whatever people say, it has been a disappointing season."
Dalglish has stated none of his big-money signings will leave Anfield this summer, despite disappointing campaigns from Stewart Downing, Jordan Henderson, Charlie Adam and Andy Carroll. Hamann raises serious question marks over whether some of the playing staff are up to the job.
"Are the players going to improve that much in the second season? Maybe," Hamann said. "Can you bring new players in? Not sure how much money you've got to spend.
"But the improvement has got to come from somewhere, because the teams that finished 15 points ahead of you, they'll be spending £30 million in the summer.
"It's a vital summer for the football club to make the right calls, because it's now three years running [that Liverpool have not finished in the Champions League places] and obviously the longer you go without any Champions League, the further you fall behind.
"The best players won't come to your club and you probably can't afford them anyway because there is so much money in the Champions League.
"For a team like Liverpool to be out of contention in March or April - finishing 15 or 16 points behind fourth - is just not good enough. If you miss out on the last day of the season by three or four points, well, that happens to a lot teams.
"But to be out of contention by March or April, with eight or nine games to go, and not having a chance of finishing fourth, that's not acceptable."