SAN FRANCISCO, Calif. ( TheStreet) -- Mannkind ( MNKD) said late Friday that U.S. drug regulators are extending the review of its inhaled insulin device because an inspection of a third-party manufacturing facility is not yet complete. The U.S. Food and Drug Administration was expected to issue an approval decision on the Mannkind diabetes device, now known by the brand name Afrezza, on Jan. 16. But Friday, FDA officials informed Mannkind that an inspection of a manufacturing plant owned by Organon that makes the insulin used in the Afrezza device was not complete. Organon is a subsidiary of Merck ( MRK). Mannkind said it does not know how long the FDA's review of Afrezza will be delayed. Mannkind investors -- both bulls and bears -- were anxiously awaiting the FDA's Jan 16 decision on Afrezza, so Friday's announcement is a bit of a letdown. Mannkind shares fell 5% to $7.60 in Friday's after-market trading session after finishing the regular session at $8.04. The FDA delay is also somewhat of an embarrassment for Mannkind executives who have boldly predicted FDA approval of Afrezza on Jan. 16. Last week, CEO Al Mann and COO Hakan Edstrom gave separate media interviews expressing confidence that the FDA's review was essentially complete and that approval was coming. Mannkind officials are presenting at the J.P. Morgan Healthcare Conference Tuesday. Investors will surely be asking why Mannkind didn't know that the FDA's inspection of its outside insulin supplier was not yet complete. A person close to Mannkind told me Friday night that FDA inspectors, in fact, had already visited the Organon insulin plant, located in France, and no questions or concerns were raised, leading Mannkind to believe that the inspection was done. The company was therefore surprised Friday when FDA told them that inspectors needed to revisit the Organon plant to complete inspection on a part of the facility that was missed during the previous visit. "The FDA messed up," said the person close to Mannkind, who asked to remain anonymous because the company doesn't want to anger the agency while the Afrezza review remains open.