The clubs are separated by one point and one place in the table, and Hill is full of admiration for what London Welsh have achieved during their debut top-flight campaign.
Worcester's opponents have already won four games this term - one more than the ninth-placed Warriors - and are 13 points clear of bottom club and relegation favourites Sale Sharks.
"London Welsh have had a very good season and cannot be underestimated," Hill said.
"Most people wrote them off before the season started, so it is credit to the coaching staff and players that they have played with no fear and have got their tactics right against most teams.
"They were promoted to the league late on, so to arrive where they are is an outstanding feat, and they already have some big scalps.
"They will have identified this game as one that is winnable, so we have got to be top-notch to get a result."
Captain and lock James Percival returns to the Worcester starting line-up as one of four changes from last weekend's 13-6 Amlin Challenge Cup defeat in Perpignan.
Wing David Lemi is recalled, while full-back Chris Pennell and centre Josh Matavesi also feature as Worcester look to extend an unbeaten home record stretching back until early September.
London Welsh head coach Lyn Jones has named a side showing 13 changes after last weekend's Challenge Cup home loss to Grenoble, with only full-back Tom Arscott and centre Seb Jewell retained.
And there is a start for scrum-half Rob Lewis, a recent addition to the London Welsh squad on loan from Cardiff Blues.
"Worcester have stabilised in the Premiership and are now taking their game on to another level of accuracy which is required in this league," Jones said.
"We realise we have a lot of work to do to gain an understanding of what the important ingredients are in the Premiership.
"A win away from home against this side would be a huge achievement for us as a team."
Friday's game will be the first between the clubs at Premiership level, but they have met 18 times in lower divisions, with Worcester on a run of 17 successive victories.
London Welsh's only league win against the Warriors produced a 28-13 scoreline in National One at Sixways more than 15 years ago.
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