It's not so much the injury to Emerson,I'm sure Blasi and Appiah/Tacch could hold the fort for two matches.
But Mascherano does provide something extra.He's comfortable on the ball and can distribute leading up to the attack,and although he's a good ball winner contrary to what has been said here he isn't all that similar to Emerson in style.He isn't as boisterous or aggressive and prefers to read situations rather than rush in and take charge like the Brazilian does.