Saracens sweat on Brits fitness ahead of semi-final
The 36-year-old hooker is set to retire at the end of the current campaign, having been a key figure in the London club's rise during the past eight years, including their back-to-back European titles in 2015/16 and 2016/17.
Saracens thrashed visitors Gloucester 62-12 on Saturday and will be back at their Allianz Park ground in a fortnight for a Premiership semi-final with Wasps.
But they may be without the dynamic Brits, capped 10 times by the Springboks, and Wales international Liam Williams who was one of seven try-scorers against Gloucester.
"Schalk has a hamstring problem and Liam has a shoulder problem and it's too early to assess the seriousness," said Saracens director of rugby Mark McCall.
Sarries scored nine tries – Ben Spencer crossed twice and the hosts also managed a penalty try – against an outclassed Gloucester, but McCall was far from happy with his side's display.
"We didn't work hard enough in the first half and they [Gloucester]scored two wonderful tries," he said.
"They were terrible for us though so we spoke at half-time that we needed to take it to a higher level," the former Ireland international added.
"We learnt a good lesson at Leinster in the [European] Champions Cup as it showed you don't get any second chances and you can't afford to switch off momentarily."
Saturday's final round of regular-season league games saw Wasps win 39-22 at Newcastle.
But coach Dai Young was concerned by the way his side almost squandered a 31-3 lead to let the Falcons back in at 31-22 before a late try from South Africa fullback Willie le Roux put the result beyond doubt.
"We aren't going to win at Saracens with a 60-minute performance like that," said Young.
"We need to play for 80 minutes and we will have to be at our best at Allianz Park – I want us to go there and perform. That's the challenge and we have to be up for it," added the former Wales and British and Irish Lions prop forward.
Despite their defeat, Newcastle can still look forward to a semi-final against reigning champions Exeter.
Newcastle director of rugby Dean Richards was forced into making eight changes against Wasps, but the former England No.8 expects to have a fully-fit squad to select from in two weeks' time.
The options going into the semi-final at Exeter will be totally different for us – we will have a few players to come back in and we will step it up," he promised.
Exeter ran in six tries as they pulled away late on to win 41-17 at Harlequins.
One of those tries was a superb score by 21-year-old flyhalf Joe Simmonds, who is vying for the No.10 shirt with veteran playmaker Gareth Steenson.
"Joe is going very well," said Chiefs boss Rob Baxter. "There will tough selection decisions between him and Gareth for the semi-final – the guy that has been there and done it against the guy who has got the shirt at the minute."