Franco van der Merwe has stepped down as captain of South Africa's struggling Super Rugby team the Lions, saying he wants to focus on improving his own performance.

The second-rower said on Thursday he had been battling for form and needed to "focus on my own game right now".

The Lions said centre Doppies la Grange would take over as skipper of a team which has won just one of its last 20 Super Rugby fixtures, losing five out of six games this season.

The Johannesburg outfit went winless in last year's Super 14, the first time a team has lost 13 games in a Super rugby tournament.

Van der Merwe backed La Grange ahead of Saturday's game against Queensland.

"Doppies has been playing some very good rugby and is a good leader," he said.

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