Lannan was ready to take the reigns as the fifth starter in the Nationals' dominant rotation while Chien-Ming Wang recovers from a hamstring strain.
Adam Kilgore of the Washington Post reported that Lannan was sent down and that Ross Detwiler will likely become the Nationals' fifth starter.
Detwiler has shown good control this spring. In 17.2 innings, Detwiler has struck out 18 while walking five batters. He has pitched to a 3.06 ERA while giving up 14 hits this spring.
The 26-year-old Detwiler has not thrown more than 75.2 innings in his career but has a chance to impress the Nationals while Wang is sidelined.
Lannan had drawn interest from teams all offseason but the Nationals ultimately decided to keep Lannan around. They will have a decision to make down the road, assuming they hold on to Lannan and Wang becomes healthy.
They are one of the few teams that have depth at pitching and can withstand injuries to their starting rotation.
Lannan had a chance to start the season with the big club due to Wang's injury but now finds himself in Syracuse. Perhaps his 5.14 ERA in spring led to the decision to be made.
Now it is up to Detwiler to impress with the opportunity he has been given and force manager Davey Johnson to make a decision when Wang returns.