Meredith (Ellen Pompeo) and Derek (Patrick Dempsey) may face a big challenge in their relationship when Grey's Anatomy returns.

Before the show's winter finale, Derek turned down an offer to partake in a prestigious study for Meredith. But, after he received a phone call from the President of the United States to join him on a brain mapping project, it may be impossible for him to turn it down.

"I can tell you that everything kind of gets turned upside emotionally because of the President's phone call to Derek," Sarah Drew, who plays April on the show, told Glamour. "All kinds of things get messed up because of that phone call."

April's Choice Between Jackson And Matthew Will Leave 'A Lot Of Regrets'?

The President's phone call may put a damper on the relationship between the two doctors. But, will Derek really take on the President's offer and leave the hospital?

Another relationship is also in focus when the show returns - April and Jackson's.

"It's incredibly tense and there are going to be a lot of regrets either way," actor Jesse Williams, who plays Jackson, recently told TV Guide of April's choice.

Williams also teased that his character will face new challenges at his job.

"He is really going to have to find a balance between his personal relationships and his bias and the fact that the Avery Foundation runs everything, but he's very junior to some of the other attendings," he said.

Grey's Anatomy returns for the second half of season 10 on Thursday, Feb. 27 on ABC.