He has been placed in charge on a temporary basis, with Chris Ramsey shown the exit after guiding the club to just two wins from their past 10 games.
It has been an eventful week for QPR, who sacked head coach Ramsey on Wednesday evening, before announcing that former manager Warnock would take charge on an interim basis.
Ramsey had been appointed as the club's full-time manager in May, singing a three-year contract upon their relegation from the Premier League, but life in the Championship has proved tough for the West Londoners.
The R's have suffered six defeats in their opening 15 league outings, with three of those losses coming in the past five matches.
Their poor form eventually cost Ramsey his job, and a 1-0 defeat against Derby County on Tuesday evening proved to be his last game as manager.
Many of the club's problems this season have stemmed from their poor defensive record, and with 24 conceded, only three teams in the division have leaked more goals than they have.
Recent form: LDWLL
Hoping to take advantage of the turmoil at Lofus Road are a Preston outfit who have started to find their form after a difficult spell on their return to the Championship.
The Lilywhites had actually gone unbeaten in their first three league games, but a winless spell of nine matches soon followed, with five of those outings ending in defeats.
However, they have put together a run of five games without being beaten, and the latest of those ended in a 1-0 victory over Nottingham Forest on Tuesday evening.
Although Preston may have one of the least effective attacks in the league, with only 11 goals scored, they have proved solid at the back and have shipped a meagre 13 goals, which is the lowest number of any team in the bottom half.
Recent form: DWDDW
Warnock could be tempted to make a number of changes in his first game back at QPR, but he will be unable to call upon the services of James Perch, who was shown a straight red card late on against Derby.
Meanwhile, Grayson may stick with the same lineup that saw Preston beat Nottingham Forest in midweek, with Eoin Doyle retaining his spot up front after netting his first goal for the club.
On-loan goalkeeper Jordan Pickford will also keep his place in the side, having kept five clean sheets in his last five games.
QPR possible starting lineup:
Green; Onuoha, Hill, Hall, Konchesky; Henry, Faurlin, Tozser, Suk-young, Phillips; Austin
Preston possible starting lineup:
Pickford; Vermijl, Woods, Wright, Cunningham; Browne, Johnson, Gallagher, Reach; Garner, Doyle
Head To Head
Preston have endured a poor run against QPR in recent meetings between the teams and they have claimed just one victory in the previous 10 games.
We say: QPR 1-1 Preston
It is difficult to see what impact the managerial change will have at QPR, but the club need an improvement after back-to-back defeats. All of the uncertainty will surely give Preston confidence of causing an upset, and we think that the visitors will come away from Loftus Road with at least a point this weekend.