Cramer originally thought Nike would push the index above that mark, but after seeing some tech stocks rally Wednesday and a positive note about LinkedIn, he set his eyes on the Windows software-maker.
"When you see Western Digital go up and Micron [Technology] go up, you say how far can this extend?," Cramer said. "Well, if it extends to Microsoft, then Microsoft can be a big enough factor in this endless pursuit of Dow 20,000."
Microsoft, which acquired LinkedIn this year, is expected to report earnings at the end of January. If Microsoft is the key to the Dow crossing the 20K level, that may mean the index won't hit its milestone until the new year.
On Thursday, the Dow opened lower, pulling further away from 20,000. On Wednesday, the index closed about 60 points away from the level.
—CNBC's Fred Imbert contributed to this report.