"I would say Ryan is more likely to play against the Springboks at the minute," said Wales team manager Alan Phillips. "Ryan's done a fair bit of running."
Another Lion, prop Gethin Jenkins, has already been ruled out of the opener as he continues his recovery from another calf injury. Jenkins has not played for Wales since last November, following toe surgery in January.
Wales are confident the trio will all be fit in time for the second round clash with Samoa.
"They're progressing well and hopefully they're going to be fit for selection, if not for this game then definitely for the second game," said Warren Gatland.
But their sole focus is on Sunday's clash with the Springboks and Phillips insists Wales are relishing the big kick-off.
"It's the right time for us to play them but we will never lose sight of the fact that they are a formidable outfit," said Phillips.
"There's no fear now. We respect them and although they haven't had a good run this is the Rugby World Cup so we know what to expect.
"I'm sure they also respect us but right now we are focusing on preparing our own game. The results have been close the last few times we have played them and that is going to help our confidence."