The Reds sold the Brazil international in a £142m deal to La Liga champions FC Barcelona in the January transfer window.
Coutinho’s departure left a void in Jurgen Klopp’s midfield that has been filled by Alex Oxlade-Chamberlain and Milner.
Emre Can’s persistent injury problems have allowed the German head coach to play his English trio of Jordan Henderson, Milner and Oxlade-Chamberlain in the middle of the park.
They were vital in Liverpool FC’s 5-1 aggregate win against Premier League title winners Manchester City in the Champions League quarter-final earlier this month.
Milner was outstanding in Liverpool FC’s 5-2 victory over Serie A side AS Roma in the first leg of their Champions League last four on Tuesday night, although his handball gave the Italian side a lifeline.
The 32-year-old has scored one goal and has made 11 assists in 41 games in all competitions this season.
Former Irish defender Cunningham believes Coutinho’s transfer has allowed Milner to flourish in Klopp’s team.
“Milner has gone to the next level since Coutinho has gone,” Cunningham told Irish radio station Newstalk.
Liverpool FC will take on 19th placed Stoke City in the Premier League at Anfield on Saturday afternoon.
The Reds haven’t won the Champions League title since 2005.
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