That is the warning from Reds legend Phil Thompson.
Jurgen Klopp spent a massive fee of around £65million – a world record until Chelsea bought Kepa Arrizabalaga for £72m this week – to land the Brazilian from Roma.
The German had long identified Alisson as his first-choice goalkeeping target this summer to solve Liverpool’s long-term problems in the position.
Karius appeared as though he could provide the solution to the issue last term after replacing Simon Mignolet as No 1 in January.
But after a promising five-month spell in the first team, the shot-stopper suffered a horrendous display in the Champions League final – committing two errors as Liverpool lost 3-1 to Real Madrid.
That performance alone saw widespread calls for Klopp to recruit a new goalkeeper and while he initially loathed to meet Roma’s price demands, Liverpool eventually agreed a deal after Karius suffered another moment to forget in a pre-season friendly with Tranmere Rovers.
Yet while Alisson’s arrival will allow Karius to step out of the limelight and slowly regain his confidence, Thompson has warned the incoming keeper that despite the excitement over his signing – he too will face close inspection at Anfield.
“This fella has kept [Manchester City’s] Ederson out of the national side so he is a good goalkeeper,” ex-defender and caretaker manager Thompson told Sky Sports News.
“No matter how much you pay, not just for a goalkeeper but even an outfield player, you don’t know what they’re going to be like, particularly when they come from abroad, and how they’re going to react in the Premier League.
“If he copes, he does the business and saves us points, I think with what we’ve got offensively it could be a fantastic position.
“In midfield we needed a bit of an aggressor and Naby Keita brings that.
“I know it’s not right but he was sent off four times last year so a little bit of nastiness quite helps in the side – plus he gets goals – and Shaqiri will bring goals from midfield.
“But that [in goal] was the main position for Liverpool.
“If Alisson can do it and accept all the pressure that the Premier League and being a Liverpool goalkeeper will bring because they’ve been watching Karius for every mistake and save he made.
“That will be exactly the same for Alisson but it’s a big, big chance for him in the Premier League.”
Liverpool have been tipped to challenge City for the Premier League title this term following their summer business, despite the fact Pep Guardiola’s side finished 25 points ahead of them last season.
But Liverpool beat City in three of their four meetings across all competitions last season and with their improvements, Thompson believes they can close the gap at the top of the table.
“That is a massive area and if Liverpool go on and win the league title, that will be incredible and he [Alisson] will be the signing of the window,” the former captain added.
“I know it’s a lot of money but that is where it lies. We’ve seen how well David De Gea has done at Manchester United, the points that he’s saved.
“If Alisson can do that at Liverpool because offensively, we’re up there with Manchester City quite easily, quite exciting, but that was one area that needed to be sorted.
“Liverpool have done their business nice and early unlike some clubs who have been caught out. For Liverpool I think it’s been a fantastic window.”