The former West Ham goalkeeper thinks the Spanish giants could afford to buy both superstars.
Neymar is set for an unprecedented £199m switch to Paris St-Germain after the French outfit triggered his release clause.
But Hislop thinks Barca should move for Mbappe ahead of Coutinho if they opt to sign just one replacement.
He told ESPN FC: “I think it’s huge. If you have the choice of one of Mbappe or Coutinho, Mbappe is your winner for me even though he may be a solid £50m more.
“I think you go for Mbappe, that means Liverpool maybe breathe a sigh of relief.
“They can afford both.”
When pushed on his suggestion Barca could sign both Mbappe and Coutinho, Hislop added: “I was just pointing out that they’ve got an awful lot of money.”
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New Barca manager Ernesto Valverde is desperate to strengthen his side after they lost out in La Liga last season to Real Madrid.
And they were also forced to watch their rivals win the Champions League after their exit in the quarter-finals.
Barca have made two signings so far this summer in bringing Nelson Semedo and Gerard Deulofeu to the Nou Camp.
