The Argentinian had expressed an interest to return to South America earlier this year, but the club refused to let him leave.
When asked about the 31-year-old at his pre-match press conference, the manager said: "I don't know how to put that into words, really. He is very, very important, a very steady, calming influence.
"Last year when he wasn't playing, there was something missing from the team. That's why it's so important that he stayed, and hopefully he will stay for a lot longer than this year as well."
The Magpies travel to Everton on Monday.