Speaking to Entertainment Weekly, McKidd explained that the couple's problems will begin to escalate as the season comes to a close.
"Everything's in a state of flux... but I think they're getting down to the nub of what's going on between Cristina and Owen," he said.
"There are some tough times ahead of them. I think people need to strap in a little bit because it's going to get pretty bumpy for a while between these two."
McKidd claimed that one of Owen's "biggest frustrations" is Cristina's inability to communicate, and added: "I imagine it's going to raise some pretty interesting debate. Who's right and who's wrong - or is anybody right? It's definitely going to be an, 'Oh my God!' type thing. It's definitely going to be pretty life-changing for them - the final moments of the finale."
However, McKidd also suggested that Cristina and Owen will manage to work out their problems in the future.
"I don't think their wedding was their happy ending," he said. "But I think that eventually - through a lot of tough make-it-or-break-it moments - I'd like to believe that they'll end up old and grey together."
Grey's Anatomy continues on Thursday at 9/8c on ABC in the US and on Wednesday at 10pm on Sky Living in the UK.
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