The Paris St.-Germain players, champions of France and riding high on a surge of investment in women’s soccer, were in fine spirits as they enjoyed a dinner with club officials last week in a restaurant close to one of the city’s largest parks.

Months removed from the squad’s first French title, regulars in Europe’s biggest tournaments and unbeaten in the new season, the team had much to celebrate, and the mood was collegial. As the night out wound down, one of the team’s new signings, Kheira Hamraoui, accepted a ride home from her teammate Aminata Diallo. Car-pooling made sense; both women lived in Chatou, an upscale suburb on the outskirts of Paris, and soon they and a third player were in the car for the half-hour drive home.

As the car approached Hamraoui’s house around 10.30 p.m., however, the journey took a menacing turn. Two masked men emerged from the darkness and dragged Hamraoui out of the passenger seat. Then, according to news media reports later confirmed by the French police, the men beat Hamraoui with a metal bar for several minutes, paying particular attention to the part of the body she most needed to play for one of European soccer’s most successful women’s soccer teams: her legs.

When the beating ended, the men ran off. Diallo, who had been restrained, was apparently unharmed.

By Wednesday, she was a suspect in the attack.

Early Wednesday morning, the French police arrested the 26-year-old Diallo at her home nearby and confirmed in a statement that her detention was related to Hamraoui’s complaint, though they did not explicitly link Diallo to the assault, and refused to comment for the record. The French sports daily L’Equipe, which first reported the arrest, suggested Diallo may have played a role in the attack on Hamraoui, her rival for playing time in the center of the P.S.G. midfield.

Even before then, though, the attack had been the talk of training facilities across Europe, where multimillion-dollar investments in women’s soccer have raised the profile of the sport, its best players and its biggest clubs. That has raised the stakes for players who now see the sport as a viable profession and a potential route to riches for the very best performers through six-figure annual contracts and growing sponsorship opportunities.

While the club hired additional security for Hamraoui’s worried teammates, the police investigation quietly gathered pace. On Wednesday, the arrest of Diallo shook everyone anew.

“Paris St.-Germain is working with the Versailles police to clarify the facts,” the team said in a statement. “The club is paying close attention to the progress of the proceedings and will study what action to take.”

Noël Le Graët, the president of the French soccer federation, expressed shock at the arrest of Diallo, who like Hamraoui has played for France’s national team. Diallo was in camp with the team as recently as last month, for a set of World Cup qualifiers. Hamraoui, a veteran of the 2015 World Cup and the 2016 Olympics, last played for France in 2019, but her career had been revived by a Champions League title with Barcelona last season and an off-season move to P.S.G.

“What is suspected is implausible,” Le Graët said. “I know both players. I am appalled if what is mentioned is true. It seems unimaginable.”

The incident and the accusations of personal rivalry and professional jealousy immediately evoked memories of the 1994 assault on the figure skater Nancy Kerrigan, who was attacked at that year’s United States championships in a plot orchestrated by the ex-husband of a rival skater, Tonya Harding. Kerrigan was assaulted after a practice session by a man who hit her repeatedly in the legs with a police baton.

After Kerrigan was forced to withdraw from the championships because of her injuries, Harding won the competition and earned a place on the 1994 U.S. Olympic team. Kerrigan was later named to the team as well, and several weeks later she won the silver medal at the Lillehammer Games. Harding, who has long denied being involved in the attack but pleaded guilty to hindering prosecution, finished eighth.

The scandal was revived in 2017 with the release of a fictionalized biopic, “I, Tonya.”

P.S.G., backed by the deep pockets of its Qatari owners, said Wednesday that it was continuing to provide its players with added security in the days since the attack, an extra layer of protection that it regularly arranges for its well-known men’s players. Several P.S.G. players have in recent years had their homes robbed — sometimes while family members were inside — while they were away playing matches.

“Since Thursday evening the club has taken all necessary measures to guarantee the health, well-being and safety of its entire women’s team,” the P.S.G. statement added.

For many in women’s soccer, though, the Hamraoui incident was hard to comprehend. The motivation did not appear to be robbery — the assailants had taken nothing from either of the women, the police said — but rather a single-minded effort to injure a player.

Competition for places in the team’s lineup has increased this season after the women’s team finally ended the dominance of its league and continental rival Lyon by winning its first French title. P.S.G. had finished second to Lyon eight times in the previous 10 years. With a domestic title in hand, the team now has a European club title firmly in its sights.

Signing Hamraoui, 31, from the European champion Barcelona for her second stint with the club was part of P.S.G.’s efforts to strengthen its team, and to defend its sudden primacy in its ongoing domestic rivalry with Lyon. Both teams have started the new campaign as strong as ever, with each having won its first seven games. P.S.G. has yet to surrender a goal in domestic or European competition.

Diallo also returned to Paris this season, after a loan to Atlético Madrid, but has effectively been used as Hamraoui’s understudy. That changed this week when Hamraoui, badly shaken and nursing cuts and bruises — but no broken bones — was unable to play in a Champions League game against Real Madrid.

At the time, the club explained her absence as a personal issue. Her replacement in the lineup on Tuesday? Diallo.