WASHINGTON -- Left-hander Gio Gonzalez may be pitching for his spot in the Washington rotation when the first-place Nationals begin a four-game home series Thursday against the Cincinnati Reds.

Gonzalez will get the start opposite left-hander Brandon Finnegan of the Reds, who are last in the National League Central by a wide margin.

The game comes two days after the major league debut of Nationals right-hander Lucas Giolito, 21, who showed that he is ready for the bigs by throwing four scoreless innings and allowing just one hit to the New York Mets. Giolito did not return after a fourth-inning rain delay in a game the Nationals won 5-0.

When ace Stephen Strasburg (10-0) returns from the disabled list, the Nationals could be faced with a pleasant quandary: send Giolito back to the minors, mostly likely to Triple-A Syracuse, or keep him in the rotation and send Gonzalez to the bullpen.

That may be a long shot since the Nationals already have three lefties in the bullpen and general manager Mike Rizzo may want to keep Giolito fresh for a September appearance -- perhaps as a bullpen stopper or spot starter because he is on a innings limit.

How would Nationals manager Dusty Baker compare Giolito to other pitchers?

"Four innings is not enough to judge," Baker said. "I don't really like to make comparisons because it is not really fair."

Gonzalez was acquired by the Nationals in a deal with the Oakland A's after the 2011 season. The veteran from suburban Miami won 21 games in 2012 and helped Washington win the National League East title. However, he couldn't keep the lead in Game 5 of the National League Championship Series against the St. Louis Cardinals, and long-time fans of the Nationals have not forgotten that game.

The next three years, Gonzalez went 11-8, 10-10 and 11-8 with ERAs between 3.36 and 3.79.

This season he is 3-7 with a 4.73 ERA in 15 starts. He has lasted less than six innings per start and has reached the 100-pitch mark by the fifth inning on occasion.

He has given up 89 hits (nine homers) and 28 walks with 88 strikeouts in 85 2/3 innings. The Nationals have lost his last seven starts, and Gonzalez is 0-6 in that stretch.

Mets infielder Asdrubal Cabrera was teammates with Gonzalez in Washington for part of the 2014 season.

"He knows what he has to do. He enjoys this game a lot," Cabrera said.

Finnegan, who came up through the Kansas City system, pitched against the Nationals last September at Nationals Park when Max Scherzer took a no-hitter into the eighth inning. That was the day after reliever Jonathan Papelbon went for the throat of teammate Bryce Harper in the Washington dugout late in the game.

In 16 starts this year, Finnegan is 3-6 with a 3.83 ERA. He held the Nationals to one run in 6 1/3 innings June 3 at Cincinnati in a 7-2 victory.

The Reds are 29-50 after a loss on Wednesday afternoon to the Chicago Cubs. To make matters worse, center fielder Billy Hamilton was banged up while going for a ball hit by Anthony Rizzo that became an inside-the-park homer.

Hamilton left the game in the first inning, and he was diagnosed with a facial contusion. He is in concussion protocol for the second time in 2016.

"It didn't get him in the eye or the nose. It was more on the cheek," Reds manager Bryan Price said. "I saw him in the fourth or fifth inning, and he was in pretty good spirits. He wanted to stay in the game, but in that situation, we made the best decision."

Nationals manager Dusty Baker, who was Cincinnati's manager from 2008-13, said late Wednesday it will not be hard to be ready for the Reds.

"That is no problem, keeping them motivated," he said of his Washington players. "You can't overlook anybody. The Reds almost swept us in Cincinnati."

The Reds won the first two games June 3-4 before the Nationals won the finale 10-9 on June 5.