The New York Yankees have a 3.5 game lead for the first American League Wild Card spot, but might have to fend off opponents without their best pitcher for a few weeks. 

According to Jack Curry of YES Network, New York's manager Joe Girardi announced that ace Masahiro Tanaka has a grade 1 hamstring strain and will miss at least his next start, if not more. 

Tanaka was slated to start the final game of a three-game series between the Yankees and Toronto Blue Jays. The Yankees are behind by three games in the American League East, but are still projected to make the playoffs with a Wild Card spot. 

The injury that will keep Tanaka out for at least his next start is a hamstring strain, which was acquired when running the bases on Friday. 

Ivan Nova will start on Wednesday in the place of Tanaka. 

"It's frustrating," Girardi said. "But we have to deal with it, and Nova's going to have to step up for us on Wednesday. Hopefully [Tanaka] will just miss the one turn."

Nova, 28, was demoted from the starting rotation just a week ago, but has struggled all season. Over 75.2 innings pitched (14 games), Nova is 6-8 with a 5.11 ERA. He was very dominant in 2011, but has gotten worse and worse ever since he finished fourth in the American League Rookie of the Year voting that season.

Girardi noted that it would probably be smarter to have him skip a start and make his return rather than start against Toronto and severely injury his hamstring. He does not want his ace to get knocked out for the season, especially not with his team in an opportunity to possibly make a deep playoff run. 

"Maybe it's just something tight," Girardi said. "And he pitched well [after the injury]. But our fear is that if he goes out there on Wednesday, he could hurt it worse. And then you're in a whole lot of trouble."

Tanaka was running the bases because he got his sixth plate appearance all season long. 

"You get concerned whenever your pitchers have to hit, and you try to do everything you can to keep them from getting hurt," Girardi said. "The one thing you can't prepare for is that sudden burst that they have to make. We tell our guys to take it easy in situations, but I've often said that one of the reasons they are successful is their competitive nature inside of them. He's someone who has hit in the past, and you feel that he's pretty comfortable doing it, and it didn't work out."

The returning MRI showed a grade 1 hamstring strain, which is not severe. To compare, Yankees lefty Chris Capuano was diagnosed with a grade 2 hamstring strain and was forced out for the first six weeks of the season. 

"I'm not looking at it as something very serious," Tanaka said through an interpreter. "The reason I say that is because I hurt it early in the game and felt strong enough to continue. If I felt that it was something that I could not have handled, then I would not be in that game."

The 26-year-old from Japan is 12-7 on the season with a 3.88 ERA. He was not chosen as an All-Star this season, but was picked last year, which was his rookie season. Tanaka has tossed 149.0 innings over 23 games for the Bronx Bombers.