I interviewed for two positions at the same time, one internal and one external. It looks now like I am going to receive offers from both, but my preference is for the external position. Right now I have received the external position offer in writing but I need to clear a background check which will take about 2-3 weeks. The hiring manager for the internal position sent me an email today saying he wants to meet sometime in the next week to hash out details.

What is the best way to turn down the internal offer without hurting my relationships in the company? I can’t officially resign till my position until I clear the background check, but I wouldn’t want to waste the hiring manager for the internal position’s time unnecessarily either.