12 Dec, 14:42
Prop Cian Healy is expected to miss the start of the 2014 RBS 6 Nations after undergoing surgery on his injured ankle on Wednesday.
But an insect bite to his right hand means Powell's participation in the game is in some doubt.
Meanwhile, Ulster and Ireland flanker Stephen Ferris, who was hoping to make his Lions bow off the replacements bench, may also have to give his place up.
Ferris sustained a calf muscle strain in training and both players will undergo fitness tests tomorrow morning before any decisions are made.
Lions scrummaging coach Graham Rowntree said: "We've got a couple of niggles. Andy Powell picked up a bit of a hand injury this week, and didn't train fully this morning. We will assess that tomorrow morning.
"And Stephen Ferris has got a bit of a calf injury, which we will assess tomorrow as well.
"We've got a great medical team, and we are certainly not ruling people out the day before a game.
"We've got various contingency plans. With all the back row options we have, we can make decisions on the day of the game."
The Lions are gunning for a morale-boosting win in tomorrow's game, with Ireland out-half Ronan O'Gara, who will be partnered by Scotland's Mike Blair at half-back, eager to get the tour off to a solid start.
"Everyone wants to get on the pitch as soon as possible. We've had a fair bit of training and a fair bit of fitness training," said O'Gara, one of four Irish players in the side to face the Royals.
"So it's nice now to get into a contact situation, a game, because you can do as much training as you want but essentially the first real test comes on Saturday and this will set the tone for the tour.
"The mood in camp is great. With the less numbers, the management have done a really good job with that and fellas really feel part of it.
"I think everyone genuinely feels they have a crack off the Test team, which is what you want."
Saturday's opponents, all full-time professionals, will be no pushovers. They include 11 players from the Griquas side and are captained by Leopards flanker Wilhelm Koch.
Koch, a relative of Springbok prop Chris Koch who played against the Lions 54 years ago, said: "We want to win just as much as the Lions do. Our opponents have 10 fixtures, but we have only one and for most of my team this is the match of a lifetime.
"My team are both nervous and excited. We know the Lions have stars aplenty, but they should not underestimate us. We are looking forward to a very physical encounter."
The Royal XV coach Chaka Willemse, who is also from the Leopards, feels his players will give the tourists a tough opening encounter.
"We have a lot of experience up front and backs who like to move the ball. The temperature in Rustenburg has been 26 degrees all week and I will not be surprised if the heat gets to the Lions," he said.
"We are hoping for a sell-out crowd of 42,000, something we would have achieved easily had not the Super 14 final between the Bulls and the Chiefs been scheduled for the evening, and the atmosphere at the ground will be electric.
"Our job is to make it as difficult as possible for the Lions by playing good rugby. They will be in a battle, but one which will be within the rules of rugby. My players know I will not tolerate any gratuitous violence."
The Lions' opening match of the 1997 tour to South Africa saw them claim a 39-11 win over an Eastern Province Invitation XV, while in 2001 in Australia Ronan O'Gara helped himself to 26 points in an 18-try demolition of Western Australia. The final score was 116-10.
Four years ago, Brian O'Driscoll captained the Lions to a 34-20 opening win over the Bay of Plenty in New Zealand but the match was marred by a tour-ending ankle injury for flanker Lawrence Dallaglio.