By SABC Sport
2nd February 2024
The Algeria international underwent a medical on Thursday but the switch appeared to have been called off by West Ham, with Lyon describing the club's behaviour as "incomprehensible" and lacking respect.
The French side maintained that they had filed the relevant information in time for the deal to be ratified, and called on the world governing body to intervene.
The Hammers confirmed on Friday afternoon that Benrahma's loan move for the rest of the season with an option to buy had indeed gone through.
The PA news agency understands the club rejects Lyon's accusations that West Ham acted improperly, which it believes are unfounded and potentially damaging.
Pablo Fornals has also left the club to join Real Betis after the LaLiga side joined Lyon's appeal to FIFA over why a deal that appeared to have been completed was on the brink of collapse.
A move had looked set to go through on Thursday but Betis claimed "a computer problem" prevented the transfer from being completed.
Betis CEO Ramon Alarcon told Spanish reporters: "There was a last-minute problem with Fornals, we think it was a computer problem.
"Betis sent all the documents correctly and on time and it seems West Ham had a computer problem."
It brings to an end four-and-a half year stay for the Spain international at the London Stadium.
He made 203 appearances after joining from Villarreal in 2019, including 151 in the Premier League, scoring 23 goals.
His most famous strike for the club was the one that secured a first-leg victory against AZ Alkmaar in the Europa Conference League semi-final last season, en route to the team winning their first European trophy in almost 60 years.
Benrahma leaves having made 146 appearances for the club after arriving from Brentford in 2020, 105 of which were in the Premier League.
Both players had slipped down the pecking order in David Moyes' squad this season.
Speaking after the team's 1-1 draw at home to Bournemouth on Thursday night, Moyes said of Lyon's comments: "(Lack of respect) is a big word to use before we get a chance to show exactly what happened or didn't happen.
"It's something we've never had to deal with before and I'm an experienced manager."