Arsenal boss Arsene Wenger describes the decision to let midfielder Abou Diaby leave the club as one of the "saddest moments" for the club.
The 29-year-old was tormented by injuries during his Arsenal stay and never managed to enjoy regular first-team football in the Frenchman's squad.
He left the club after his contract expired at the end of last season.
"It's one of the saddest moments for us at Arsenal not to have had the opportunity to get the best out of Abou Diaby because of injury," Wenger told the club's official website.
"I'm very sad because this boy is a massive and a huge talent. It's sad as well because he didn't deserve what he got. It's sad as well because he's a very serious player.
"He was always at home every night, prepared well every day and was not rewarded.
"I hope he will be rewarded somewhere else in the final years of his career.
"He was the closest to Patrick Vieira we have seen here, with even a good offensive potential. In France, he's regarded highly because every time he played in the French national team he made a difference. It is very sad."