Mascherano joined Liverpool from West Ham in January.
Xabi told the Sunday Times: “He plays like a 30-year-old. He has a cool mind on the pitch. He is analysing and thinking about the game in each moment.”
He added: “West Ham were in a difficult position, everything was going wrong, and in that situation it’s difficult for any player to play at their level. It’s been important for Javier to prove he can play well for a team like Liverpool.”