Chico, who is scheduled to start Sunday's game against San Francisco, was 5-7 with a 4.96 ERA in 25 starts before being optioned to Columbus on Aug. 17. He made a pair of Minor League starts, tossing six scoreless innings against Louisville on Aug. 22 and giving up four runs in five innings Monday at Indianapolis.
Chico, 24, was the only Nationals starter to not miss a turn in the rotation until he was optioned.
Manager Manny Acta said he wants to see the Chico that gave the Nationals quality starts during the first half of the season.
As for Abreu, this will be his second stint with Washington. He went 2-0 with four saves and a 1.57 ERA in 27 games with Columbus after being designated for assignment June 20.
Abreu, 30, went 0-1 with a 6.38 ERA in 19 big league appearances during his first tour with Washington. Abreu has posted a combined 104 strikeouts in 76 1/3 innings with Washington and Columbus, an average of 12.3 strikeouts per nine innings pitched.
Bill Ladson is a reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.