Wales coach Warren Gatland has hailed 20-year-old Williams' impact during World Cup preparations, which move up a gear next Saturday with a warm-up clash against England at Twickenham.
Henson has made only one international appearance in more than two years due to injuries and then a self-imposed exile from rugby before he started playing again through short stints with Saracens and Toulon.
Despite his lack of game-time, the former Ospreys centre is widely expected to feature in Gatland's 30-man group for New Zealand, which will be announced on August 22.
Jamie Roberts and Jon Davies seem shoe-ins for two of the centre berths, and with James Hook a proven Test centre or fly-half, it could be that Henson finds himself vying for a place with the likes of Williams.
"He (Henson) will hopefully get an opportunity," said Gatland, looking ahead to World Cup preparation fixtures against England (home and away) and Argentina this month.
"He is in a position at the moment where there is good competition.
"You've got Jamie and Jon Davies as probably the established partnership. Gavin comes in, and we've been incredibly impressed with Scott Williams.
"Scott hasn't played a lot of rugby at this level, but we have been impressed with his skill levels and the way he reads defence. He has definitely got something to his game.
"He is a player to watch out for in the future.
"Whether he gets opportunities in the next few weeks and the World Cup, he has given a few headaches at the moment with the way he has impressed us at training."
Gatland, meanwhile, is hopeful captain Matthew Rees will be fit to lead Wales at the World Cup next month despite being laid low by a neck problem.
Scarlets hooker Rees has already been ruled out of Wales' trip to Twickenham, with flanker Sam Warburton set to skipper the side.
Gatland admits that surgery is a possibility for Rees, who has won 46 caps and was appointed Wales skipper last November.
But the 30-year-old is due to undergo injections in the hope it will relieve pressure on his neck, with any operation not taking place until after the World Cup.
"An operation is a possibility, but we are hoping it definitely won't be before the World Cup. If he doesn't improve, he may need something after the World Cup," added Gatland.
"There is a bit of nerve pressure, and we are hopeful the injections will help.
"He is getting a little bit agitated at the moment because he hasn't been able to do much in the last couple of weeks and he can see the players going away from him a little bit."
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