But in the four starts since, three of which came on four days' rest, Tanaka was 1-3 with a 4.25 ERA, five home runs allowed and 22 strikeouts in 29 2/3 innings, a ratio of 6.67 per nine innings.
On Tuesday night, Girardi downplayed the effect of pitching on a standard big league schedule for Tanaka's decline.
"I don't know; it's hard to say,'' Girardi said. "It's the first time that I think he's gone a couple of starts like this on five days, so it's an adjustment."
Tanaka, who was named to the American League All-Star team in his first major league season, was scheduled to pitch Sunday in the Yankees' final game before the break. Now it is unknown when, or if, he will pitch again this year.
It is a blow to the Yankees, who already have lost three of their starting pitchers to injury -- Ivan Nova (Tommy John surgery), Michael Pineda (back muscle strain) and, most recently, CC Sabathia, who is suffering from swelling in his right knee that could require microfracture surgery. He likely is done for the season.
In their absence, the Yankees had cobbled together a rotation of two rookies ( Vidal Nuno and Chase Whitley) and third-year man David Phelps, who lost out to Pineda in a spring training competition for the No. 5 starter's job, to go along with 39-year-old Hiroki Kuroda. Last week, the Yankees traded Nuno to the Arizona Diamondbacks for Brandon McCarthy, who started Wednesday night's game against the Indians.
But Tanaka was the glue who was holding the rotation and the team together; the Yankees were 13-4 in his first 17 starts. He had been acquired after a bidding war with a half-dozen other big league teams for his services following a 24-0 season in 2013 for the Rakuten Golden Eagles, and he was signed to a seven-year, $155 million contract this winter.
"It's a loss right now, and if he's gone for any length of time, I mean, it would be a big loss,'' Girardi said. "What he's done for us, the innings and the quality of starts, it's hard to replace.''
Girardi said he was likely to use Whitley and a combination of relief pitchers to get through Sunday's game, but he did not know what the Yankees would do if Tanaka is out for significantly longer than 15 days.
"Let's just get through Sunday, and we're going to have to figure out what we're going to do after that,'' he said. "Pitching is fragile. I think you have to be fortunate to have five starters give you 30 starts a year in this day and age. I can't really tell you why. It's not how you draw it up, I can tell you that. But injuries are part of the game, and you've got to deal with them.''