Portsmouth have completed the signing of France midfielder Lassana Diarra from Arsenal for an undisclosed fee.The 22-year-old only joined the Gunners from Chelsea last summer but has been frustrated by a lack of first-team opportunities at the Emirates Stadium. Diarra will join his new team-mates for training tomorrow and could make his debut in Saturday's Barclays Premier League match at home to Derby. Paris-born Diarra began his career with Le Havre before moving to Chelsea in 2005. He was named the club's young player of the year after his first season but made just 31 appearances in two years and agreed to a £2million move to Arsenal. Redknapp believes he has pulled off a coup in landing the player. He told the club's website: 'He's a fantastic midfield player. 'In my opinion he's already one of the best midfield players in the Premier League and has the ability to be one of the best there is. 'He's strong, powerful, quick and can pass the ball. You don't play for France for the last nine or 10 games unless you're top quality. 'I'm delighted he has decided to sign for us rather than a host of other clubs. It's great news for Portsmouth Football Club.'