He departed Anfield for Barcelona in 2010 for £20million.
Mascherano, asked how much Liverpool have improved this season, said: "Very much. They are a very good side. And I am very happy for the lads because I still have some friends at the club like Steven Gerrard and Lucas.
"So what is happening now is not only good for the club but good for them, too.
"They have been there a long time and deserve this. I enjoyed my time there. Liverpool are a top club and must always be in the top four of the Premier League. Always.
"I think they will finish in the top four this season. I have seen a lot of their games and I am very impressed with the way they are playing."
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