It's his second stint with the Nationals this season. The NL East leaders selected his contract from Double-A Harrisburg on June 6 and Ross went 2-1 with a 2.66 ERA in three starts.
The 22-year-old rookie is filling in for right-hander Stephen Strasburg, who went on the disabled list July 5 with a strained left oblique.
Due to an off-day and the All-Star break, Washington hasn't needed a fifth starter until now. Manager Matt Williams said the plan is to have Ross remain in the rotation until Strasburg returns.
Strasburg on Tuesday threw his first bullpen session since going on the disabled list and reported no issues, according to Williams.
The Nationals optioned infielder Wilmer Difo to Harrisburg.