<human>: Background: Shoaib Akhtar ( pronunciation ; born 13 August 1975) is a former Pakistani cricketer, who played all formats of the game for fourteen years. He is the fastest bowler ever in the history of cricket, who delivered the fastest delivery officially recorded at a top speed of 161.3 km/h in a pool match against England in the 2003 Cricket World Cup. Akhtar was nicknamed as "Rawalpindi Express" & "Tiger", as a tribute to his hometown and fast bowling. He is the first bowler to break the 100 mph barrier as well, which he did twice in his career.
Context: Akhtar made a return to international cricket albeit in the shorter format of the game. In May 2010, PCB named him in a list of 35 probables for the Asia Cup. On 15 June 2010, Akhtar made his return, taking 3 wickets for 28 runs in the first match of the Asia Cup against Sri Lanka. He narrowly missed out a spot in the 2010 ICC World Twenty20 in place of the injured Umar Gul.  In July 2010, he was selected for the Twenty20 series against Australia but the selectors decided not to play him in the Test squad so that he would not get injured. He was subsequently selected for the ODI and Twenty20 series against England in September 2010.  Akhtar returned to the national side representing the country against England in the Twenty20 International. He bowled an impressive spell and returned with figures of 2 wickets for 23 runs. He continued to bowl well in the ODI series in the absence of regular fast-bowlers, Mohammad Asif and Mohammad Amir, who were suspended by the International Cricket Council amid allegations of Spot-fixing. Despite his relatively good bowling form, Pakistani coach Waqar Younis insisted that the bowling attack must not become reliant on Akhtar, as he is 35 years of age and fitness troubles continue to affect him. Akhtar was selected for the tour of New Zealand and started his campaign off well with 3 wickets on Boxing Day in the first of two Twenty20 Internationals against New Zealand.  Akhtar was selected in Pakistan's 15-man squad to play in the 2011 World Cup hosted by Bangladesh, India, and Sri Lanka in February to March. During the tournament, he announced that he would retire from international cricket at the end of the World Cup. He was dropped from the squad after group matches and was not included in the quarter final either. In September, Akhtar released his autobiography, Controversially Yours. CANNOTANSWER
Question: What was his rehabilitation for?

Answer:
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