Barca have committed to a fee rising to €160m to sign Coutinho last month.
“I think if you lose your best player there's no way you can dress it up as a positive window," Carragher said on Sky Sports' The Debate show.
“To lose him mid-season, I don't agree with it but for that fee… Coutinho's not worth that. He's not that good.
“I would have took £20m-£30m less in the summer to know that Liverpool would have had him for the second half of the season because at that time we were still in the FA Cup, still a Champions League to play for."