John Toshack says Jurgen Klopp's future at Liverpool cannot be guaranteed unless he wins a trophy this season.
Klopp steered Liverpool into the final of the Champions League last season, and the Reds have followed that up by making their best start to a Premier League campaign with 33 points from 13 games.
But Klopp has failed to land a trophy in his three years at Anfield – and former Liverpool favourite Toshack feels the German must do that this term to make life easier for himself on Merseyside.
"If Liverpool don't win a trophy this year then they've got a decision to make (about Klopp)," former Real Madrid and Wales manager Toshack said.
"Things look really good at the moment, but this is Klopp's third full season at Liverpool and this is the acid test for him.
"You can be unlucky not to win a trophy, but at the top clubs that's what matters.
"It's such a fine dividing line, but when you're at a club like Liverpool that's what it's all about."
Former Borussia Dortmund boss Klopp initially agreed a three-year deal to become Liverpool manager in October 2015.
He signed an extended six-year deal in July 2016, with Liverpool's American owners saying it would have been "irresponsible" not to offer Klopp a long-term contract.
Unbeaten Liverpool currently trail champions Manchester City by two points, and have a huge Champions League trip to Paris St Germain on Wednesday.
"Klopp seems a super guy," Toshack told Press Association Sport.
"He's open with the players and tells it how it is.
"Maybe he's too passionate at times, but the dividing line is so thin between first and second.
"You feel City have got the edge with Pep Guardiola because they've got trophies behind them.
"That's a big thing and Liverpool haven't won any yet."
Toshack's own journey from Cardiff to Liverpool, Madrid and many other stops far and wide is told in a new book which chronicles an extraordinary career.
The former Liverpool striker took Swansea from the old fourth division to the first, managed Real Madrid twice, and has worked in 10 different countries.
But the 69-year-old Welshman feels his last job at Iranian club Tractor Sazi, which he left in September, could mark the end of over half-a-century in football.
"I don't think I'll ever lose my love for the game, it's been my life, but when you're approaching 70 years of age it's not the same," Toshack said.
"I don't see myself having too much more time in this profession, and the last job might be it.
"I found that one really difficult. It was a new club taken over by Iranian people from Turkey who knew of me from my days at Besiktas.
"In six league games we won two, drew three, and lost one – and, with a new club, that wasn't such a bad start.
"But I think they thought 'Toshack's coming in and we'll win the Championship before Christmas'.
"It didn't work out like that and I'm finding that part of the job a lot harder than I did years ago."
:: John Toshack was speaking at the book launch of 'Toshack's Way: My Journey Through Football', which is published by deCoubertin Books and costs £20
ga('create', 'UA-72310761-1', 'auto', {'name': 'pacontentapi'});
ga('pacontentapi.set', 'referrer', location.origin);
ga('pacontentapi.set', 'dimension1', 'By Phil Blanche, Press Association Sport');
ga('pacontentapi.set', 'dimension2', 'd703e17c-a0cc-41d4-993c-5f1a402e57e7');
ga('pacontentapi.set', 'dimension3', 'paservice:sport,paservice:sport:club-news,paservice:sport:football');
ga('pacontentapi.set', 'dimension6', 'story');
ga('pacontentapi.set', 'dimension7', 'composite');
ga('pacontentapi.set', 'dimension8', null);
ga('pacontentapi.set', 'dimension9', 'sport:football');
ga('pacontentapi.send', 'pageview', { 'location': location.href, 'page': (location.pathname + location.search + location.hash), 'title': 'Trophy crucial to Klopp\u2019s Anfield future, warns Toshack'});
