While all eyes are usually on the payroll increase in the monthly jobs report, noted Wharton School finance professor Jeremy Siegel said the unemployment rate is what investors should watch for in Friday's report.
Most Fed officials believe an unemployment rate in the 5.0 to 5.2 range is consistent with full employment.
"If we see 5.1 tomorrow morning I think the odds of a Fed increase in two weeks goes way up," said Siegel.
Mark Zandi, chief economist of Moody's Analytics, told CNBC on Wednesday after the ADP jobs report was released that the unemployment number will almost certainly be going to 5.2 and may go to 5.1. Siegel believes Zandi is one of the best forecasters.