Reina is adamant that Mascherano's departure will hurt the Reds as he is such an important part of the line-up as well as a great person off-field.
"The departure of Mascherano is a big problem for Liverpool is a big problem because he is one of the best players of his type on the pitch," the Spanish gloveman said.
"Javier is very competitive, very Argentinian and he always offers his maximum in every game. For Barca this is a good new thing, but it's not for us.
"Mascherano will be a positive surprise in La Liga. He is a footballer who works, works and works. Also, personally, he is a good character. He is quiet but very friendly.
"He was not someone who got into controversy. He never caused rows in the dressing room. He was good on the pitch, broke up counter attacks and now we need other players with his characteristics."