Diallo, who was arrested on Wednesday at her home near Paris, was driving Hamraoui home last week when the star midfielder was pulled from a car by masked men and beaten with a metal bar.
Although seen as friends who socialised and even holidayed together, police had focused on a possible sporting rivalry that had led to violence, which Diallo denied while in detention.
A man already in jail for a separate assault case in the southeastern city of Lyon -- a friend of Diallo's -- had also been arrested as part of the investigation, but he was also released on Thursday evening.
"The club remains by the side of its players to enable them to come through this challenging time and help them find peace of mind," PSG said in a statement late on Thursday.
French media reported that Hamraoui had raised the alarm about Diallo when she filed a police complaint about the attack, highlighting the unusual route taken by her teammate and the slow speed of their vehicle when the attackers sprang out.
Diallo, 26, who was described as cooperative while in custody, explained that she was driving slowly because the street was narrow, l'Equipe newspaper reported.
Both players were absent from team training on Friday and a scheduled media event by the team has been cancelled.
Diallo and Hamraoui were interviewed together on Thursday at a police station in Versailles, just outside Paris, which enabled investigators to compare their versions of events, while a third player, Sakina Karchaoui, was also called to make a statement.
The incident has sent shockwaves through the Qatar-owned club, which has ploughed money into its women's team which won the league title last year for the first time.
They are set to play arch-rivals Lyon on Sunday in a table-topping clash in the French women's league.
Neither Diallo nor Hamraoui attended the team's training session on Friday, the club said.
- Questions -
Given the manner of the attack on Hamraoui and the arrest of Diallo, commentators recalled a notorious assault on American ice skater Nancy Kerrigan in the run-up to the 1994 Lillehammer Winter Olympics.
Her rival Tonya Harding was banned for life after her ex-husband and bodyguard hired a hitman to club Kerrigan in the leg.
Hamraoui, a 31-year-old French international returned to PSG last summer from Barcelona, where she won the Champions League last year.
She was recalled to the French national team in October after an absence of more than two years, but pulled out because of injury.
Diallo, who has been capped seven times by France, was called up to replace her in the squad, but was not used by coach Corinne Diacre.
Hamraoui, who needed stitches after the attack last week, was absent from the PSG team which beat Real Madrid in the Champions League on Tuesday, with Diallo taking her place in central midfield.
French football has also been rocked in recent years by allegations that star attacker Karim Benzema took part in an attempt to blackmail national teammate Mathieu Valbuena with a sex tape.
Benzema, who went on trial last month, denies the allegations. A verdict is expected on November 24.
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