Saracens have confirmed George Kruis was knocked out in their defeat at Harlequins

Kruis was struck by a swinging arm by James Horwill just 90 seconds into the title clash at Twickenham Stoop and was tended to by medics for eight minutes before being carried off on a stretcher.

The England second row, who is expected to start the RBS 6 Nations opener against Scotland on March 6, will now be assessed ahead of Saturday's Champions Cup clash with Ulster.

Horwill was sent to the sin-bin for the offence, but Saracens director of rugby Mark McCall refused to question whether the former Australia captain should have been sent off.

"George is fine. There is nothing wrong other than the concussion. He was knocked out. He'll do the normal checks," McCall said.

"I don't know when a yellow becomes a red. For us to lose George Kruis in the first minute to a swinging arm....I don't know where the boundaries are."

In a stormy but pulsating clash that saw Saracens' 15-match triumphant run come to an end, Rhys Gill was sent off in the 65th minute for his role in a spear tackle on centre George Lowe.

Gill was assisted by prop Petrus du Plessis as Lowe was picked up and dropped on his head, but it was the replacement hooker who was shown a red yard by referee Craig Maxwell-Keys.

Maxwell-Keys initially brandished a yellow before changing his mind upon repeat viewing of the incident.

"I think it was a red card. There are no complaints. Rhys has just come on to the pitch, he's trying to make a good tackle and someone else is involved," McCall said.

"It made it look worse than it is, but you always run the risk in those situations."

Saracens remain at the summit of the Premiership, but their lead has been reduced to three points after the only unbeaten record in Europe's top three leagues fell.

"In general we didn't deserve to win. Our discipline wasn't good enough. They won the scraps and were really up for it," McCall said.

"All those 50-50 battles that we're pretty good at, we weren't so good at. It's disappointing to lose."

Harlequins director of rugby Conor O'Shea believes the calls made by Maxwell-Keys at the key moments of the match were correct.

"A huge turning point was Rhys' sending off, but I don't think you could argue with that," O'Shea said.

"I'm just thankful George Lowe did not suffer anything because we all know what he has been through over the last three years.

"I'm really thankful that there was nothing wrong with George Kruis but when you look at the actual play, James is coming in and he is going to clear a ruck.

"Kruis is going down and there is nothing malicious in it but we have to protect players so we will take the yellow.

"It was a great game of rugby between two teams who will hopefully be fighting it out towards the end of the year."