The Slovenian has been in possession of the red jersey since Stage 10, with the event concluding in Madrid on Sunday.
However, he also enjoyed some fine form at the Giro d'Italia this year before eventually finishing third and Valverde, who is currently second in the general classification, is hoping that history will repeat itself.
"Anything can happen. The leader could have a bad day or we could lose time. Third weeks in Grand Tours can cause problems for anybody," the Movistar rider said.
"We have to be realistic, and Roglic is going very well, but sometimes we've seen him crack at this point in a race."
Valverde finished 18th in Stage 16 but remains optimistic that the final week will go his way.
"It's true we lost some time yesterday, and it wasn't my best day, but if I look at the day before, it went a lot better," Valverde said.
"I'm going into this final week feeling optimistic."