The Red Devils have gone six matches without a win in all competitions for the first time since 1998 and exited the Champions League at the group stage following a 3-2 defeat at Wolfsburg on the final matchday.
Van Gaal has faced criticism from some supporters over his style of play, and the Dutchman admitted that he is worried about his future following Saturday’s 2-1 reverse at home to Norwich, the Canaries' first win at Old Trafford since 1989.
Should the 64-year-old depart, outgoing Bayern Munich boss Guardiola is the most popular choice to take the reins, with more than 50% of 1,865 fans polled backing the ex-Barça boss and two-time Champions League winner.
Pep could potentially have the pick of Manchester United, Manchester City, Arsenal and Chelsea in the summer, while Jose Mourinho is also in the running for the United post having left Stamford Bridge earlier in December.
Just 20% of Forza Football voters favour the Special One pitching up on Sir Matt Busby Way, 3% more than Van Gaal's assistant Ryan Giggs.
WHO SHOULD REPLACE VAN GAAL?
Pep Guardiola 51%
Jose Mourinho 20%
Ryan Giggs 17%
Carlo Ancelotti 6%
Diego Simeone 3%
Other 3%
Carlo Ancelotti, who will take over from Guardiola at the Allianz Arena in time for the 2016/17 season, received 6% of the vote, with Atletico Madrid head honcho Diego Simeone next with 3%.
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