The South Korea international has been dealing with a troublesome foot problem for a few weeks and was also missing from the 1-0 Europa League quarter-final second-leg win over Eintracht Frankfurt on Monday.
Postecoglou told reporters in Saturday's press conference that he could not put a timeframe on Son's recovery, while James Maddison is unsurprisingly a doubt after being wiped clean out by Frankfurt goalkeeper Kaua Santos in midweek.
Maddison's sacrifice was worthwhile, as Dominic Solanke scored the resulting penalty that sent Spurs through to the semi-finals, and the ex-Liverpool starlet should be one of the few starters retained from that win.
Mathys Tel is another, as the Frenchman bids to become the first teenager to score in three straight Premier League matches for Tottenham, but Wilson Odobert could push Brennan Johnson out of the side.
A fit-again Dejan Kulusevski should be a straight swap for the sore Maddison in the middle, while the fresh legs of Pape Sarr and Yves Bissouma should also be utilised from the off.
Postecoglou may not shy away from a full complement of defensive changes too, as Kevin Danso, Ben Davies, Djed Spence and Archie Gray benefit from the tight turnaround.
Tottenham Hotspur possible starting lineup:
Vicario; Gray, Danso, Davies, Spence; Kulusevski, Bissouma, Sarr; Odobert, Solanke, Tel
Written by
Ben Knapton