Hills limped off with a knee injury in the first half of last weekend's home game against Hartpury.
'Although Michael will miss the Richmond game the injury is not as bad as we first feared and he's only expected to be out for three to four weeks,' said head coach Glen Kenworthy.
Samoan international Josh Tyrell, who came on for Hills, is expected to start.
'He played more minutes than we probably wanted him to (in his first game back) but he made a big difference when he came on and he's not suffered any reaction,' said Kenworthy.
Knights could also lack fly-half Kurt Morath who picked up a knock in Saturday's game.
'We'll probably make a late decision on Kurt,' said Kenworthy.
Charlie Foley is expected to take over the No 10 shirt if Morath, who impressed Kenworthy on his starting debut with his tactical kicking, is ruled out.
Young back-rower Sam Jones, who suffered a head injury in the final warm-up game last month, is also still out.
Better news for Knights is that full-back Paul Jarvis and wing Curtis Wilson, who have yet to play this season due to hamstring injuries, are both available for selection.
'There is a lot of competition for places in the backs,' said Kenworthy, who remains in charge due to the absence of director of rugby Clive Griffiths.
Although Knights will fancy their chances of back-to-back wins, Kenworthy says there will be no complacency.
'Obviously we are looking to build on the win over Hartpury and get some momentum but we are taking nothing for granted because they pulled the wool over our eyes twice last season,' he said.
'They play a brand of rugby which if you get sucked intoÂ they can beat you and we are aware of that. They aren't a flashy team but they play for the full 80 minutes.'
Kenworthy took in Richmond's encounter against Yorkshire Carnegie at Headingley on Sunday and felt the 24-7 scoreline, boosted by two late tries, didn't reflect the game.
'They've got a nuggety pack and they've got a very good scrum-half who runs the show and if we can't shut him down we could be in for a long afternoon,' he said.
Griffiths is scheduled to have an operation todayÂ to fit a stent after suffering a suspected heart attack last week. The 64-year-old is expected to make a full recovery.