Last updated on .From the section Rugby Union

Billy Vunipola "stitched himself up" by injuring his hamstring before the semi-final with Wasps

Billy Vunipola says kicking an Australian rules football was behind his most recent injury.

The Saracens number eight, who heads to South Africa with England on Saturday, had to come off at half-time in the Premiership semi-final win over Wasps with a hamstring problem.

But Vunipola, 25, was fit enough to play 60 minutes in Sarries' Premiership final win over Exeter on Saturday.

He said: "It was my fault, I was doing AFL kicking and the hammy went tight."

Vunipola added: "I trained fully the week before against Wasps [in the play-offs] and I felt really good.

"I didn't tell the coaches that, but when I came off at half-time against Wasps I told them. I was like, 'sorry guys, I was doing AFL kicking'. I stitched myself up there.

"I had to manage myself a bit better the week after. Now I feel strong again."

Vunipola, who has had an injury-interrupted season, has not played Test rugby since March last year, but is part of a 34-strong England squad aiming to win a series in South Africa for the first time.