Saracens start their European Champions Cup defence against Toulon on Saturday and could welcome England fly-half Owen Farrell back into the fray.
Farrell has been out of action since August because of back problems, and the return of a player Sarries director of rugby Mark McCall described as "the best in Europe" would be a welcome boost as they start their quest for a second straight title at the home of the three-time European champions.
"Owen is world-class, the best player in Europe in my opinion," McCall said. "He has been training regularly over the last three weeks and he is a big game player, so there are lots of things in his favour to pick him.
"There are players who can come straight back and Owen is one of them.
"He is one of the fittest guys I have ever seen, so that doesn't come into it. It obviously makes it hugely tempting for us to start him if he is OK.
"He didn't react well after last Wednesday's session but he's much more in contention this week. He's been all good with his kicking and he's done some tackling as well, so hopefully he'll be available. It's quite a big shout."
Saracens have made an excellent start to the new Premiership season, sitting two points clear at the top having won five of their opening six matches - easing to a 30-14 bonus-point victory over Wasps last time out.
The tournament favourites can afford to have confidence of making an early statement of intent at the Stade Mayol, with Toulon losing three of their opening eight Top 14 games.
Scarlets and Sale Sharks make up the rest of Pool 3 while last year's runners-up Racing 92 have been grouped with Glasgow Warriors, Leicester Tigers and Munster - who visit the defending French champions on the back of a 25-14 Pro12 loss to Leinster.
Leinster's bid to win Europe's premier club competition for the first time since 2012 starts against Castres, with Northampton Saints and Montpellier the other two teams aiming to progress from Pool 4.
Pool 5 consists of Pro12 leaders Ulster and Top 14 pacesetters Clermont Auvergne, who visit Bordeaux Begles and Exeter Chiefs respectively in their openers.
Defending Pro12 champions Connacht host Toulouse in Galway, while Wasps face Zebre in the other Pool 2 clash.
Connacht have never gone beyond the group stage of the tournament and are a lowly eighth in the Pro12 after five games.
But coach Pat Lam is upbeat about the Irish province's chances against a Toulouse team with a size advantage.
He said: "There's opportunities there. It goes back to the way we can play the game, if we can put pressure on by keeping ball, or kicking well, or defending well on the gain line, that will give us a chance."