The 23-year-old signed a five-year deal with the Merseyside outfit last week after Liverpool agreed a £4.7m fee with Bundesliga club Mainz.
Karius has already been handed the number one shirt in a clear sign that Mignolet is facing a battle to remain in Jurgen Klopp’s starting line-up.
The Belgium international has been the first-choice goalkeeper at Anfield since his £9m switch to the Reds from Sunderland in 2013 despite his error-strewn performances.
New Liverpool signing Karius warned Mignolet that the German youngster is determined to established himself as Klopp’s first-choice goalkeeper.
“I wanted the No. 1 shirt because I was wearing it at Mainz,” Karius told Liverpool’s website.
“And I want to be the No. 1 here at Liverpool.”
Liverpool conceded 50 goals in 38 Premier League games in the 2015/16 season with Mignolet in goal for the Merseyside outfit.
The Reds lost 3-1 to reigning champions Sevilla in the Europa League final in Basel earlier this month.
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