The 36-year-old Italian joined the Aviva Premiership club from Gloucester Rugby in 2009.
"I'm really excited for the rest of the season, and to be honest I don't feel like I'm retiring yet, it hasn't crossed my mind," Nieto told Sarries' official website.
"I'm only thinking about preparing for the next few games which will hopefully bring the club more success.
"It's close to the end of my career and I've been extremely lucky that at the end of my time here in English rugby, that I have been able to play for the best team in England."
Nieto was part of the Saracens team that won the Aviva Premiership title in 2011.