Dragons number eight Wainwright avoided a suspected broken cheekbone but has suffered a nasty gash.
“The main issue was a fracture,” said Humphreys.
“He doesn’t have that fracture, so we are pretty hopeful he will be available.
“He had an unbelievable gash. That’s the thing for us. He’s a tough kid and he’s like ‘I’ll be alright, they can just stitch me back up’ but it’s a pretty bad gash.
“He’s got eight days to turn around so we are hopeful, especially since he’s desperate to play.”
Scarlets back row Taine Plumtree has been flown in to join up with the squad while James Botham switched from flanker to number eight for the game in Paris.
Cardiff number eight Faletau has not played an international since the World Cup pool victory against Georgia in October 2023, the last time Wales won a Test match.
Gatland’s side have since suffered 13 successive international defeats, including seven Six Nations losses on the bounce.
The defeat in Paris was the first time Wales had failed to score in a tournament match since 1998, while it has been 18 years since they finished pointless following a 31-0 loss to Australia in 2007.
