In the last season finale, Cristina (Sandra Oh) discovered that she was pregnant but rowed with McKidd's character Owen over whether or not to go through with it.
McKidd has now told TV Line that whether the argument is "just a bump in the road, or... a real block in their relationship" will be explored during the beginning of the new season.
"The writers have written Cristina into a bit of a box," he said. "The really good juicy stuff gets going when they go, 'OK, we're going to make this as difficult as we possibly can for this couple'.
"They fought to get together, with the Teddy of it all in season six and then the PTSD, and now it's like, 'Slam, we're going to give you the hardest problem of all'."
However, McKidd revealed that he is enjoying the scenes, saying: "It just gives us an opportunity to tell a better story and a more important story. And it's really tough. Network shows aren't dealing with that topic of conversation about abortion. I think it's cool that they're not skirting around it."
Cristina is expected to make a decision about her pregnancy in the upcoming season premiere, but McKidd has previously warned that "it's not going to be easy" for Cristina and Owen.
Grey's Anatomy will return for a new season with a two-hour premiere on September 22 on ABC.
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Watch a trailer for the new season of Grey's Anatomy below: