The 34-year-old's contract at the Veltins Arena expires at the end of the season, and he is holding out for a two-year deal.
It is understood that Schalke are only willing to offer a one-year extension, but Carvajal has confirmed that a decision will soon be made.
"Raul will make a decision in a few days. He has an offer from another Bundesliga club. But Raul wants to play only for Schalke in the Bundesliga," Carvajal told Cadena COPE.
Schalke are currently third in the Bundesliga.