Last season the club lost in the finals of the League Cup and Europa League.
Premier League stats: Most offsides so far in 2016/17
Wed, February 8, 2017
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The Reds have not won a game in 2017 and sit 13 points behind league leaders Chelsea in the title race.
Klopp refused to sign players in the January transfer window, insisting he was happy with his squad.
But Hamann has called on the German boss to rethink his plans this summer and land some big-name deals.
"Klopp has succeeded in changing a few things and now he needs to look at the playing personnel because this set of players has failed on numerous occasions in the last few seasons," Hamann told Paddy Power.
Jurgen Klopp's Liverpool side are winless in 2017
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Liverpool lost the Europa League final last season
Liverpool also lost the League Cup final to Manchester City last season
"There were times when this squad had a chance to win a trophy and they lost to Aston Villa (in the FA Cup under Brendan Rodgers in 2015), Sevilla and Southampton.
"He needs to look hard at the team, but there needs to be a thought process throughout the whole club on if they can maximise what’s possible with the players that they’ve got."