In both anime and manga, Sakuno's crush on Ryoma is clear, although she hasn't told him due to her own shy nature, some degree of bad luck and the meddling of other people (especially Nanjirō
and Momoshiro, and occasionally Kikumaru Eiji).
On the other hand, Ryoma doesn't take a possible relationship with Sakuno seriously because of his dedication to tennis.
He does however show friendly concern for her, rescuing her from bullies, offering tennis advice, and coaching her and Tomoka in tennis (albeit unwillingly; his father tricked him into doing so).