(REUTERS) - The National Women's Soccer League's (NWSL) commissioner Lisa Baird has quit and Fifa has launched a preliminary investigation in the wake of a report detailing allegations of misconduct against former North Carolina Courage head coach Paul Riley.

The world football governing body said on Friday (Oct 1) that it is "deeply concerned" about allegations of abuse in the sport in the United States.

The Athletic on Thursday had outlined allegations of sexual coercion and misconduct by Riley, who led the Courage to back-to-back NWSL championships in 2018 and 2019, after speaking to more than a dozen players he coached since 2010.

"Due to the severity and seriousness of the allegations being made by players, we can confirm that Fifa's judicial bodies are actively looking into the matter and have opened a preliminary investigation," Fifa said in a statement.

"As part of this, Fifa will be reaching out to the respective parties, including US Soccer and NWSL, for further information about the various safeguarding concerns and allegations of abuse that have been raised."

Riley, who has reportedly denied any wrongdoing, was terminated by the Courage and the league. He did not immediately respond to a request for comment.

"I am so sorry for the pain so many are feeling," Baird said in a written statement hours before she turned in her resignation and announcing that the league's weekend slate of games would not go on.

"Recognising that trauma, we have decided not to take the field this weekend to give everyone some space to reflect.

"Business as usual isn't our concern right now. Our entire league has a great deal of healing to do, and our players deserve so much better."

General counsel Lisa Levine has also left, according to the Athletic.

The report sent shockwaves through the sport and the players' association demanded sweeping changes across the league, as some of soccer's most prominent figures - including twice World Cup winners and NWSL players Megan Rapinoe and Alex Morgan - voiced their outrage.

"This pause will be the first step as we collectively work to transform the culture of this league, something that is long overdue," added Baird.

US Soccer said it would immediately launch an independent investigation into the allegations of abusive behaviour and sexual misconduct.

"Player safety and respect is the paramount responsibility of every person involved in this game," said its president Cindy Cone.

"That is true across every age, competition and ability level."

The Athletic report came days after another head coach in the league, Richie Burke of the Washington Spirit, was terminated with cause. He had previously been suspended following allegations of abuse detailed by the Washington Post.

A third coach, Christy Holly, was fired by Racing Louisville "for cause" in August; the team never revealed the reasons that led to his dismissal.