Smulders told TV Line that Robin will find it difficult to deal with Barney's relationship with Nora (Nazanin Boniadi).
"There's some pining for Barney happening at the moment," she said. "It's all about her being really depressed and not quite knowing how to tell him how she feels.
"It's a hard thing of knowing how she feels, but not knowing if it's quite right to pursue. He seems like he's really happy with Nora. He's finally in a relationship that he's seemingly very committed to seeing through."
Smulders added that Robin "doesn't like" the fact that Barney (Neil Patrick Harris) is in another relationship but explained that she is still trying to work out what to do.
"She's been quite aggressive at the moment with letting Barney know without actually saying it," she said. "I think, eventually, she'll do what she thinks is right."
Harris has warned fans that he does not think Robin and Barney will get together in the near future.
Meanwhile, last month the show's co-creators Carter Bays and Craig Thomas teased that the identity of Barney's bride will be revealed in the next season, but may not necessarily be either Robin or Nora.
How I Met Your Mother returns on September 19 on CBS.
Watch a trailer for the new season of How I Met Your Mother below: