The 36-year-old pitcher was invited to major league spring training. Hernandez was the opening day starter for Washington last season and started 29 games for the Nationals, going 8-13 with a 4.47 ERA.
Hernandez has pitched at least 200 innings in 10 of his 15 major league seasons. He last reached the mark in 2010 when he went 10-12 with a 3.66 ERA for the Nationals.
The two-time All-Star, who led the Marlins to the 1997 championship, is 174-176 with a 4.39 ERA in a career that also includes time with the Giants, Expos, Diamondbacks, Twins, Rockies and Mets.
He has appeared in 12 playoff games with a 7-3 record and 3.97 ERA.