The Champions League winner was settling into its third day near Dublin when it had to tell the League of Ireland Premier Division team that one of their players had returned a possible positive COVID-19 test.
A Chelsea spokesman said: "Earlier today, we had a possible positive coronavirus case which we are investigating. The individual has been isolated from the rest of the group.
"We also decided, as a precaution, to cancel tonight's behind closed doors game against Drogheda."
Instead of the 90-minute workout, Thomas Tuchel held another training session as he attempts to combat an already poor pre-season due to many of his players being delayed in returning after Euro 2020 and Copa America duty.
Peterborough United provided the Blues' only pre-season preparation so far behind closed doors at Cobham, which Tuchel's men won 6-1, but Chelsea still have significant work to do before their European Super Cup clash with Villarreal on 12 August (AEST).
Chelsea does, however, have additional friendlies scheduled against Bournemouth, Arsenal and Tottenham as it races the clock to get into shape for its first competitive game of 2021-2022.
Chelsea head coach Tuchel is yet to strengthen this transfer window, instead watching the likes of Fikayo Tomori, Olivier Giroud and Victor Moses seek new challenges across various leagues in Europe.