"We've had some very positive discussions," Clark said. "I continue to be very optimistic that something will get done, though nothing is done yet."
After the two sides finish up the fine print, the final step would be a physical, which could occur as soon as early next week.
Clark was a key contributor for the D-backs from 2005-07, but reluctantly left as a free agent last year, signing with the Padres after negotiations with Arizona broke down.
The D-backs re-acquired Clark last July, and he hit .206 in limited playing time.
"My role, as I understand it, would be as it has been the last five years," Clark said. "I'll be coming off the bench and spot-starting at first base and whatever else they need me to do."
What that has entailed in his time with Arizona is leadership in the clubhouse. The D-backs have a young core of position players who look up to Clark, and he was widely credited with helping teach some of the younger players like Miguel Montero how to prepare for late-inning pinch-hit at-bats.
Steve Gilbert is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.