The Chelsea striker is expected to line up for the defending Premier League champions against West Ham United at Upton Park on Saturday afternoon.
The Springboks, meanwhile, will face reigning world champions New Zealand in the Rugby World Cup semi-final at Twickenham an hour after Chelsea kick-off in east London.
And Costa, who scored in a 2-0 victory over Aston Villa at Stamford Bridge last weekend, shared a joke with some members of the South Africa squad at their Cobham training ground on Friday afternoon.
Chelsea posted the above snap on their Instagram page and wrote: “@diego.costa sharing a joke with members of the South Africa Rugby World Cup squad! #CFC #RWC2015”
Costa has scored two goals and made one assist in seven Premier League games for the defending champions this season.
The Blues drew 0-0 with Dynamo Kyiv in the Champions League on Tuesday night ahead of this weekend’s London derby.
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