Grayson knows his Saints will have to find a way past Yachvili in Biarritz if his team are to have any hope of reaching the Twickenham final, after losing twice to last season's finalists in the group stages of this year's competition.
At least Grayson knows he will be up against a familiar foe when the two teams meet for the third time in the quarter-finals.
"Their defensive system is hugely successful. they wait and wait and when you give them something they take it," said Grayson.
"In Yachvili they have probably the cleverest scrum half in the world.
"Biarritz and Toulouse away are extremely difficult games, but as Leicester proved by winning in Munster nobody's home record is there by right and surprises can happen.
"At least we have got a chance to have a go. We have got a bit of time before the quarter-finals, a couple of players coming back - it will be difficult but we will give it a go."