NEW YORK - Yankees ace Chien-Ming Wang is expected to be sidelined until at least September after injuring his foot running the bases, prompting club co-chairman Hank Steinbrenner to chastise the National League for playing without a designated hitter.

An examination in New York on Monday showed Wang partially tore a tendon and sprained his right foot Sunday during the Yankees' 13-0 interleague win at Houston. He will be on crutches and wear a protective boot for a minimum of six weeks, the latest blow to the team's banged-up pitching staff.

“My only message is simple. The National League needs to join the 21st century,” Steinbrenner said in Tampa, Fla. “They need to grow up and join the 21st century.

“Am I (mad) about it? Yes,” Steinbrenner added. “I've got my pitchers running the bases, and one of them gets hurt. He's going to be out. I don't like that, and it's about time they address it. That was a rule from the 1800s.”

Making a rare appearance on the bases at an NL park, Wang pulled up rounding third and hobbled home on Derek Jeter's single. Wang doubled over after scoring, pointed toward his right foot and was helped off the field.

“This is always a concern of American League teams when their pitchers have to run the bases and they're not used to doing it,” Steinbrenner said. “It's not just us. It's everybody. It probably should be a concern for National League owners, general managers and managers when their pitchers run the bases. Pitchers have enough to do without having to do that.”

Wang is 8-2 with a 4.07 ERA in 15 starts after winning 19 games each of the last two seasons. The right-hander will join injured Yankees starters Phil Hughes and Ian Kennedy on the disabled list.

New York reliever Brian Bruney has a similar injury to Wang's and it is uncertain when he will return.

Steinbrenner said for now, the Yankees probably will have to look within the organization to find a replacement in the rotation for Wang. Right-hander Dan Giese is one possibility.

Several attractive pitchers, including Cleveland ace C.C. Sabathia, could become available as the July 31 trade deadlines approaches.

The Yankees were off Monday and start a series Tuesday night at home against San Diego. Their win in Houston kept them six games behind first-place Boston in the AL East.

The sinkerballing Wang has been the most consistent Yankees starter over the last couple of years.

Mike Mussina and Andy Pettitte remain in the rotation, and Joba Chamberlain recently was converted from relieving to starting. Right-hander Darrell Rasner has been in a slump lately.

Wang was well on his way to helping the Yankees finish a three-game sweep in Houston when he was hurt. He'd pitched five strong innings, and scored during an eight-run burst in the sixth that put New York ahead 11-0.

Wang is 5-0 in seven road starts this season.

“It's a manager's worst nightmare when a pitcher's on a basepath,” Yankees manager Joe Girardi said after Sunday's victory. “It's unfortunate.”

After the game, Mussina summed up the problem that AL pitchers sometimes face at NL parks.

“We don't hit, we don't run the bases,” Mussina said. “You get four or five at-bats a year at most, and if you happen to get on base once or twice, you never know. We run in straight lines most of the time. Turning corners, you just don't do that.”