Reds boss Houllier is facing the prospect of losing German midfielder Dietmar Hamann and Czech playmaker Vladimir Smicer for the winner-takes-all crunch at Chelsea, where the final Champions League place is up for grabs.
There has been speculation both players could be part of a summer clear-out, but Houllier could certainly do with their involvement at Stamford Bridge. Smicer is almost certainly out with a calf injury which kept him sidelined for the weekend defeat by Manchester City, while Hamann is undergoing intense treatment on a shin injury.
Houllier said: "Didi is a major doubt at this stage. He hasn't been able to train since the City game and he'll be receiving more treatment, we want to give him every chance.
Liverpool know only a win will ensure their place in the Champions League next season, but chief executive Rick Parry has reassured Houllier there will be money to spend even if they fail against Chelsea.
Parry said: "We've got a shortlist of players it's quite a long shortlist at the moment and it's something we're working on all the time.
"I'm reasonably hopeful that the sort of players we'll be bringing in will please the fans and have them on the edge of their seats. We want them to be players who will make a significant improvement."
Liverpool have been linked with a host of players, but the prime targets are believed to be Damien Duff, Steve Finnan, Steed Malbranque, and Auxerre pair Jean-Alain Boumsong and Djibril Cisse. If Liverpool fail to beat Chelsea on Sunday, they will miss out on a Champions League windfall and be consigned to the UEFA Cup.
Parry knows Liverpool must spend wisely to improve the current squad, but added: "We will be bringing in new players.
"Money is tight in the game at the moment, but We haven't over-stretched ourselves. Failure to qualify for the Champions League isn't going to stop us spending a bit of money so our fans can be reassured on that score."
Defender Vegard Heggem, who leaves Liverpool in the summer when his contract expires after months of injury problems, will be given a trial by former club Rosenborg.
lCeltic manager Martin O'Neill has confirmed he has not signed the new contract he agreed in January.
The Hoops boss insisted it was "not a major issue" but the admission is likely to resurrect speculation he could leave the club in the near future.
O'Neill has guided Celtic into their first European final for 33 years and his team also stand a good chance of retaining the Bank of Scotland Premier League trophy they have won for the past two seasons.
Leeds, who have still to appoint a long-term successor to Terry Venables, have twice tried to lure him to Elland Road and O'Neill has already been touted as a successor to Alex Ferguson at Manchester United.
But O'Neill insisted the fact that his signature was still missing from the 12-month rolling deal announced earlier in the season was not significant even though it means he will be effectively out of contract in the summer.