Williams was forced to come off during last week’s defeat to South Africa ‘A’ after suffering a blow to the head early on.
The Lions had been expecting the full-back to be fit to play this weekend, but he still had to pass all the necessary return-to-play protocols.
Williams has now done so and he returned to full training on Tuesday morning as he bids to win a place in Warren Gatland’s team that will take on the Springboks in Cape Town.
“Everyone is all good to go. It’s only Finn [Russell] who is the only one missing out,” said Lions kicking coach Neil Jenkins.
“Liam has gone about his protocols and everything. He’s back in training. He trained this morning as normal.
“So everyone seems pretty fit and healthy, and obviously raring to go.”