Saracens' director of rugby Mark McCall refused to comment on Bulls fans booing visiting captain Owen Farrell when he was kicking at goal in his side's Champions Cup defeat.

Farrell has been frequently booed by opposition fans in recent weeks, especially during the Rugby World Cup with England, and announced a break from international rugby for his mental well-being which will rule him out of the Six Nations.

This was his first game since that announcement and the South African fans booed Farrell after a missed drop goal and when lining up a conversion towards the end of the game.

But McCall said after the 27-16 loss: "I have nothing to say about that."

Saracens denied the home favourites a bonus point in what could be crucial in the group, despite playing more than half the game with 14 men.

Billy Vunipola was sent off for contact to the head when clearing out a ruck, while full-back Alex Goode and second row Maro Itoje both saw yellow, meaning Saracens were unable to grab a losing bonus point themselves.

Saracens will be looking to bounce back when they entertain Connacht next week after the Irish side were well beaten by table-toppers Bordeaux.

McCall admitted his side had been up against it at altitude in Pretoria, with the red and yellow cards costing them.

"I think the discipline comes from pressure," he said.

"We were under a lot of pressure, we were second best physically in the first half, our breakdown and our defensive collisions were nowhere near where they needed to be.

"The scoreline was 20-6 at half-time and I think that reflected the half, but the team showed some grit in the second half to fight back when we were down to 14 men.

"It is a wonderful place to play, an iconic place to play, and we are pleased to have come here but we would have liked to have played a lot better than we did tonight.

"We've got a really important game next weekend, this competition is unforgiving - you've only got four games and we've lost the first one. We've got zero points and next week is really important.

"When you are losing collisions and under pressure then sometimes that lack of discipline happens.

"I thought Alex Goode was unlucky to be honest, I didn't agree with that decision, Billy was trying to be urgent and clear out from a line-out and got it wrong. These things happen sometimes.

"I'm pleased we fought back hard in the second half but disappointed with the first half."

*copy from PA.