The 23-year-old Belgium international was sent off by referee Michael Oliver on 52 minutes for denying Bafetimbi Gomis a clear goalscoring opportunity, with the Swans striker equalising from the penalty spot.
Blues boss Jose Mourinho refused to discuss the decision after the match, other than to suggest it “changed everything”. However, Chelsea have opted to appeal and their case will be will be heard by the Football Association today.
However, the chances of success seem slim as there has to be an “obvious error” by the officials.
Former referee Dermot Gallagher said Oliver reached the right decision.
“Not only is it a good decision, but it is excellent refereeing from start to finish,” Gallagher said.
“The overall package was absolutely complete and any young referee could learn so much from it. The penalty area line belongs to the goalkeeper; therefore it has to be a penalty. I think the fact the goalkeeper stopped Gomis is the crucial thing — he would have gone past him, he would have rolled (the ball) into an empty net.”
If — and more likely when — the appeal fails, Courtois’ expected one-match ban would see him miss the trip to last season’s runners-up Manchester City on Sunday.
Meanwhile, the Blues are understood to be close to agreeing a fee with Augsburg for the transfer of left-back Baba Rahman.
The 21-year-old has been a target for the Blues for a number of weeks and it is understood the fee will be over £20m (€28m).
Rahman’s agent confirmed earlier this month that the player had already agreed to join the Blues, having enjoyed a standout season for a side who finished fifth in the Bundesliga.
The Ghana internaitonal played 31 times and made more tackles than any other left-back in the German top division last season.
Sascha Empacher, Rahman’s representative, confirmed to German newspaper Bild last week: “It is only the clubs that have to find an agreement. We on our side are agreed.”
It is understood Augsburg were determined to bring in a new left-back before allowing Rahman to leave, and last week they clinched the signing of 21-year-old Philipp Max.
Chelsea have needed competition for their only left-back Cesar Azpilicueta after selling Filipe Luis back to Atletico Madrid, and Rahman has been their first choice.
Rahman began his career at Bundlesliga 2 side Greuther Furth, making his debut as a 16-year-old before a move to Augsburg in 2014.