The Washington Nationals are replacing their former No. 1 pitching prospect with their current one. With Stephen Strasburg officially on the disabled list , Nats skipper Dusty Baker announced Monday that they're calling up Lucas Giolito to start Tuesday against the New York Mets in his major-league debut. Giolito, 21, has been one of the most-hyped pitching prospects in baseball for the past two seasons, ranking at No. 5 on Baseball America's preseason Top 100 list. That's one notch behind Julio Urias, the Los Angeles Dodgers pitcher who debuted last month. [ Join a Yahoo Daily Fantasy Baseball contest now ]