Raul is Real's record goalscorer, having found the net 323 times during a 16-year association with the Spanish giants.
He then went on to enjoy two seasons with Schalke prior to signing for Qatari side Al-Sadd in 2012.
The 36-year-old forward expects Real to prevail in the last-16 meeting with Schalke, which takes place over two legs across February and March.
However, Raul has warned Carlo Ancelotti's side not to underestimate the threat posed by their German opposition.
The former Spain international told Real's official website: "It's going to be a special play-off for me. It's going to be great for Schalke 04 and I'm really happy that (his former) team-mates and the fans are going to experience this play-off.
"Real Madrid is better than Schalke 04, but you always have to be careful with German teams because they fight right to the end.
"They (Schalke) have a very good team as well."
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