Liverpool have completed two transfer deals in the summer transfer window so far after the Reds signed Mohamed Salah in a club-record £36.7m deal from Serie A giants AS Roma earlier this month.
The Merseyside outfit also completed a transfer swoop for England Under-20 international Dominic Solanke from Premier League champions Chelsea to bolster their attacking options.
Liverpool are also rumoured to be on the brink of announcing their third summer signing Andy Robertson from relegated side Hull City in an £8m deal ahead of the new season.
The Reds struggled badly in the second half of the 2016-17 campaign due to the absence of key personnel through injury.
Former Liverpool captain Souness has questioned the lack of arrivals at Anfield given that the Reds will be competing on four fronts next term.
“I would have liked to have seen a bit more action. I think Liverpool are still a bit off challenging for the title,” Souness told talkSPORT.
“With the demands of the Champions League next year, if two or three players get knocks and aren’t playing all the time that could badly damage them.
“I don’t think they’ve got enough strength in depth to make a real impression in the two big trophies.”
Liverpool signed seven players in the summer transfer window in 2016 as Klopp overhauled his squad following an eighth-place finish.
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