A tense 35-30 victory over Treviso on Sunday set up the Biarritz clash, with the winner topping Group Four and claiming a place in the competition's quarter-finals.
But Diamond, who hopes to have second row Simon Raiwalui and prop Cobus Visagie back from injury for the trip to the Parc des Sports Aguilera, knows there must be an improvement at line-outs and scrums if Saracens are to triumph.
He said: "Our set pieces haven't gone well in the last three or four weeks. Hugh Vyvyan took over at the line-out in the second half against Treviso and we seemed to tidy up a little bit.
"It's an area we have to work on. We are missing our two front-line locks but that's no excuse, we should be able to guarantee ourselves ball.
"In the front row we're missing Nick Lloyd and Cobus Visagie and we only carry four props anyway.
"Kevin Yates and Ben Broster do a good job when they're there but we had Arron Liffchak coming on against Treviso. He's 19 in a position which is all about experience so he's going to struggle.
"It's a worry but we've only got what we've got and must be as street-wise as we can against Biarritz."