Rio Ferdinand says the referee abused by Wayne Rooney during England's warm-up match with Platinum Stars got off lightly.

Rooney was booked for directing the phrase "fuck you" at the amateur referee Jeff Selogilwe. The England striker's subsequent apology was accepted by Selogilwe, although he warned Rooney that he could risk being sent off if he used similar language in the World Cup.

But Ferdinand, who is out of the tournament with a knee injury and has remained with England, was surprised by Selogilwe's reaction.

"I'm sure he's said a lot worse to other referees in Premier League games. Being here is magnifying things before the World Cup," Ferdinand said.

"People have to realise it was a practice match, it wasn't an official match. I don't see Wazza [Rooney] having a problem disciplinary-wise at the World Cup at all."

While Rooney and his team-mates make their final preparations for Saturday's opening match with the USA, Ferdinand reflected on the collision with Emile Heskey that left him with damaged knee ligaments.

"It was a complete freak, an accident," Ferdinand said. "The ball came in from one of the lads to Emile, I'd gone to try and tackle him from behind – he didn't actually see me coming – we both went off balance and Emile's weight went down on my knee.

"It's no fault of his at all. It's just a freak accident that could happen at any given time and it had no connection to any previous injuries I've had."

Ferdinand was aware his World Cup tournament had ended, even before he received the results of his scan.

"I knew I wasn't going to be able to play in the World Cup even before I got the scan [result] – I was just waiting to get it confirmed," he said.

"The first night was quite a pretty long night, going over what could've been and to not be able to represent your country in the World Cup."

Ferdinand will now watch Saturday's match in Rustenburg, before joining the millions in England watching the Group C fixtures with Algeria and Slovenia on television.

"It's always difficult to watch a game that you feel like you could be involved in," he added. "I'll be looking to come out again later in the tournament if the rehab allows me to do that."