The 2008 AFC Champions League knockout stage was played from 17 September to 12 November 2008. A total of eight teams competed in the knockout stage to decide the champions of the 2008 AFC Champions League.
The knockout stage involved seven teams which qualified as winners in the group stage, plus defending champions Urawa Red Diamonds.
<section begin=KSBracket/>
<section end=KSBracket/>
<section begin=QF/> The first leg matches were played on 17 September, and the second leg matches were played on 24 September 2008.
<section end=QF/>
Adelaide United won 2âÂÂ1 on aggregate.
Bunyodkor won 7âÂÂ3 on aggregate.
Gamba Osaka won 4âÂÂ1 on aggregate.
Urawa Red Diamonds won 4âÂÂ3 on aggregate.
<section begin=SF/> The first leg matches were played on 8 October, and the second leg matches were played on 22 October 2008.
<section end=SF/>
Gamba Osaka won 4âÂÂ2 on aggregate.
Adelaide United won 3âÂÂ1 on aggregate.
The first and second legs of the final were scheduled to be played on 5 November and 12 November 2008, respectively.
<section begin=Final/>
Gamba Osaka won 5âÂÂ0 on aggregate. <section end=Final/>