Despite boasting an unbeaten home record that stretches back almost four months, Bristol have slipped to ninth in the Guinness Premiership.
Saracens arrive at the Memorial Stadium on Sunday, with head coach Hill targeting a quick recovery following last Saturday's 27-0 defeat against west country rivals Gloucester.
And Bristol will need to show an improvement as they build towards Heineken Cup appointments with Stade Francais and Cardiff Blues that will make or break their quarter-final prospects.
Hill said: "We've sat down at the start of 2008 to reset our aims and objectives, and these next four weeks will define our season really.
"This period will define where we are going in the league and in the Heineken Cup, before we have a two-week break and then welcome back our injured players.
"Last week wasn't very good at all, and we let ourselves down a little bit. The effort was there - we weren't dropping off tackles, for example - but a few silly errors crept in.
"We've talked about it, but we won't dwell on it. Occasionally, it happens, but you just wear yourself down if you try to over-analyse it."
Centre Neil Brew, fly-half Jason Strange, hooker Mark Regan and flanker Joe El Abd all return for Bristol, while Andy Farrell, Glen Jackson and Richard Hill are back in a much-changed Saracens side after their surprise home loss against Newcastle last time out.
Saracens, meanwhile, have confirmed Australia's 2003 World Cup coach Eddie Jones as successor to rugby director Alan Gaffney next season.
Jones has agreed a three-year deal, while Gaffney will retain a part-time role with the club.