Keith Earls is out of contention for the second Lions game on Wednesday.
The 21-year-old suffered shoulder joint trouble during the unconvincing win over a Royal XV on Saturday and will be out for up to three days.
That would rule the centre out of Wednesday's match against Super 14 side the Golden Lions in Johannesburg.
Earls was one of several players who picked up knocks on Saturday but Lions team doctor James Robson says they are "just bumps and bruises".
Scotland scrum-half Mike Blair rolled his ankle, centre Ricky Flutey picked up a slight strain and will miss training on Sunday while skipper Paul O'Connell required anaesthetic drops to an eye abrasion.
Fly-half Ronan O'Gara took a bang on his shoulder, scrum-half Mike Phillips is progressing well from a dead leg and prop Andrew Sheridan has blisters on his feet.
Meanwhile, Robson has given a positive assessment of flanker Stephen Ferris and number eight Andy Powell after they had to pull out of Saturday's tour opener because of injuries.
Powell is back in training doing weights after picking up a hand injury while Ferris is fit again after suffering a leg muscle strain getting off the team bus last week.
"It was a bizarre injury, and an early contender for bizarre injury of the tour," said Robson.
Robson added that Wales wing Leigh Halfpenny is making progress with the thigh injury that has delayed him joining up with the squad in South Africa.
"Leigh is doing very well, by all accounts," said Robson. "He did a very good kicking session on Friday, he had a day off on Saturday, and he is now going to repeat his kicking and place-kicking session.
"If all goes well, we are looking to bring Leigh out in the middle of next week."
Meanwhile, Earls has been supported by the Lions management team following his performance in Saturday's tour opener.
The Munster back had a debut to forget, epitomising an error-strewn first-half display by the Lions but Lions backs coach Rob Howley said: "Keith had one of those games that we've all had.
"He will be disappointed. He is young, he made mistakes, but I'm sure he will bounce back.
"Every player on this Lions tour has gone out and found that, for whatever reason, the ball hasn't bounced their way. It happened to Keith on Saturday and we are not hiding away from that fact.
"Wearing the Lions badge can sometimes make you feel 6ft 8in tall, but then you go out and drop the first ball and all of a sudden you are trying to get your game back on track.
"He will be a 10 times better player for that experience and I'm sure he will bounce back and show why he was picked for the tour in the first place. The player himself and his team mates will pull him through."
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