Previous rumors suggested that the duo, who played Lucas and Peyton, would come back for an episode.
Schwahn has now told TV Line that the actors were interested in reprising their roles but will not be doing so before the end of the season. It is not yet clear whether the show will be renewed for another run.
"It's not going to happen," he said. "We won't be seeing them this year... Quite frankly, we just couldn't make a deal."
Schwahn continued: "Hilarie now has a child and a family and she's doing some nice work [on White Collar]. Chad was working on a movie down in Louisiana and there were dates we were trying to work around, but it's tricky when you try to line up all those stars sometimes.
"Everybody had the best intentions, but at the end of the day it just didn't work out."
Burton previously admitted that she did not expect to return to One Tree Hill.
The show airs on Tuesdays at 8/7c on The CW.