The fee is undisclosed, but the Daily Mail reported that the Blues agreed a £21.7 million deal for the player last week. They also revealed that the 21-year-old has signed a five-year deal with the Stamford Bridge outfit.
The Ghana international is likely to act as a replacement for Filipe Luis, who joined Atletico Madrid earlier in the summer. Cesar Azpilicueta should continue as the first choice left-back, with Rahman as a reserve.
However, if Branislav Ivanovic continues his poor performances then the Spaniard could be moved over the right, with the new signing coming in to the team in his place. The Serbia international was particularly poor during their 3-0 loss to Manchester City on Sunday.
Last season, Rahman made 31 appearance in the Bundesliga, showing he is capable of playing regularly at a high level if needed. As well as this, the defender is young enough to keep improving as an understudy to Azpilicueta, which will be a better way of backing up the 25-year-old than the 30-year-old Luis.
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