Saracens cannot overhaul Cardiff at the top of Group Three but a win tonight could see them through as one of the best-placed runners up, providing French club Colomiers do not beat Llanelli at Stradey Park.
Saracens chief executive Francois Pienaar said today: "It took us 65 minutes to get in front of Ulster when we played them at home and won 55-25.
"Very few of us have experienced Ravenhill so we can expect it to be difficult.
"We targeted four tries against Toulouse last Sunday and it was a massive achievement to make them.
"Now we have to win and ensure that we score two to four tries. It is on a knife edge.
"We have lifted our confidence because of the Toulouse game and we must keep it high."
Grewcock's last game was on 17 December and his lay-off came in the middle of a dreadful run of domestic results stretching back to mid-November. Saracens' worst display came in the recent shock defeat at bottom club Rotherham.
However, their European hopes have been buoyed by the news that Llanelli, one of the most consistent teams in the Heineken Cup, are giving free entry to spectators in the hope they will driven to a victory by a full house.
Wasps are already eliminated and because England have taken Josh Lewsey, Joe Worsley and Paul Sampson to play in the Rugby World Cup Sevens in Argentina, they will field four Under-21 players against L'Aquila at Loftus Road on Sunday.
One of the youngsters, scrum-half Alex Page, 19, will make his debut.
Meanwhile, in the European Shield, Harlequins believe they can build on their recent run of form by beating Ebbw Vale at The Stoop tomorrow, a victory which would clinch a quarter-final place.
London Irish play Piacenza at Reading on Sunday with only a slim chance of moving on.
Rugby Football Union officials today announced details of a ticket incentive scheme for the Tetley's Bitter Cup Final at Twickenham on 24 February.
Fans purchasing a minimum of four full-price adult tickets will be entitled to the equivalent number of free tickets, up to a maximum of eight, for the England-Romania clash at Twickenham this autumn.
The Cup Final is usually played in May and will revert to that date next year.
However, because this year's final between Harlequins and Newcastle is so early the RFU have set up the incentive scheme in an attempt to build a significant crowd.
