The 34-year-old joined the Bundesliga side from Real Madrid in the summer of 2010 and has had a positive impact at the club.
The Spaniard's contract set to expire but Tonnies believes Schalke will see more of him.
"I have a good feeling about his extension. Raul has only given us positive signals in the past couple of days," Tonnies was quoted as saying by Bild.
"He identifies himself with Schalke and with our fans. He is feeling very well at the club and has become an integral part of Schalke."
The 34-year-old attacker has netted 10 goals in 17 Bundesliga appearances in the 2011-12 campaign.