Klopp, initially appointed on a three-year deal in October 2015, was handed the new deal in July after the club had ended his first season eighth in the Premier League and having reached the League Cup and Europa League finals.

Liverpool, who are not involved in Europe, had appeared on course for success this season, but a dismal start to 2017 has seen them exit the EFL Cup and FA Cup as well as dropping to fifth in the table.

The former Germany international criticised Klopp in kicker magazine last week and went even further in The Sunday Times, saying the deal was "absolute madness" and adding: "They won't win anything this year and they may not finish top four."

Hamann, who won the Champions League with Liverpool in 2005, was asked about those remarks on the BBC's "Match of the Day 2" programme on Sunday after the 2-0 loss to relegation-battlers Hull, which means Klopp has now lost five of his last eight games in all competitions.

"I found it strange in the summer I've got to say because, if you look at the pure facts, Jurgen Klopp came in and I think he changed the perception in the city and the football club," Hamann, who also played for Bayern Munich, Newcastle and Manchester City, said.

"He gave them common sense and he made an impact when he came in, but if you look at the pure facts I don't think the points average has improved dramatically since Brendan Rodgers.

"You get to two finals, you lose two finals. I think they both should and could have won -- especially the second one against Sevilla [in the Europa League].

"That would have had a huge impact as they would have been in the Champions League. They have probably made a decision with their heart and not their head by extending the contract by another four years."

Hamann said Liverpool would not "get stability from a six-year contract" and must instead "get it from good work in the transfer market."

He said: "In recent years whenever the chips have been down the team have failed and that hasn't changed with Klopp.

"Whether Klopp can change it with this team, or another, I am not sure, but something has to change because the way the team is going in recent years is not good enough."