The Reds opted to let the Brazilian complete his dream move to Barcelona last week after the relentless speculation about his future at the club.
Coutinho was officially unveiled as a Liverpool FC player on Monday after the Reds agreed a fee believed to be worth around £145m with Barcelona.
Liverpool FC have already been busy in the January transfer window and have completed a deal to bring defender Virgil van Dijk to Anfield for a big-money fee.
There is inevitably set to be plenty of speculation in the coming weeks liking Liverpool FC with some attacking players as they ponder trying to sign a replacement for Coutinho rather than wait until the summer.
And former Arsenal star Merson believes that it is crucial for the Reds to bring in another attacking player to fill Coutinho’s boots this month.
Writing in his column for the Daily Star, Merson said: “Liverpool must buy in this window.
“There could be uproar if they don’t. They need to replace Coutinho, but there aren’t many players with his abilities around.”
Liverpool FC are currently preparing for their first game since Coutinho’s exit with a crunch clash against Manchester City at Anfield on Sunday afternoon.
The Reds are aiming to qualify for the Champions League for the second season running.
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