Clermont-Ferrand - England flyhalf Owen Farrell will undergo tests after hobbling off with a knee injury during Saracens' European Champions Cup defeat at Clermont on Sunday.
Farrell was forced off in the 19th minute after twisting his left knee in a collision with Clermont flank Julien Bardy.
Saracens director of rugby Mark McCall said the 23-year-old would now undergo further tests to see if he can compete in the Six Nations which gets underway on February 6.
"We can't yet evaluate the seriousness of the injury, we have to wait for the results of additional tests," McCall said after the 18-6 defeat.
Despite the loss Saracens qualify behind Clermont in Pool 1 and travel to French club Racing-Metro in the last eight.
England open their Six Nations campaign against Wales.