Isabelle Brouwers, a corps de ballet dancer who performs with Mr. Johnsey in the Mazurka in Act 3, said there had been no prejudice or hostility when he joined the company. “I think it’s a great and positive step in bringing ballet into the 21st century,” she said.

(Ms. Rojo could use some positive buzz; in January The London Times, citing unattributed sources, reported that English National Ballet had lost a third of its dancers in two years amid claims of verbal abuse, a hostile working environment and a conflict of interest in Ms. Rojo’s romantic relationship with Isaac Hernandez, a principal dancer.)

But while Mr. Johnsey’s appearance with a ballet company can be seen as a boost for gender equality, it could also be viewed as a man infiltrating an already competitive female domain. Wendy Whelan, the former New York City Ballet principal, said she had conflicting feelings.

“I don’t care what the body parts are, as long as artistically the dancer makes the choreography shine,” Ms. Whelan said. “If he is the best girl for the job, then great.” But, she added, this could be “another hurdle” for women in a field that is more difficult for them to succeed in than men. “Living the life of a woman in ballet means not having access to the privileges that come with the patriarchy,” she added.

And Isabella Boylston, a principal with American Ballet Theater, said that she didn’t see an issue “if they are open to it going both ways” and have women in male roles too.