If a baby boy is unwell, the Milah (circumcision) is postponed. When the child is well, the postponed Milah may not be held on Shabbath. The Taz quotes the Bedeq HaBayith who says that when a Milah has been postponed, it should not be held on Thursday either, on account of the pains that occur on Shabbath since one should not cause suffering on Shabbath. He adds, that it would appear that one should especially not do it on Friday either.
A question arises in a case where the child has become well and is fit to have the Milah performed. If the parents went ahead and organized the Milah for Thursday or Friday, should the Mohel refuse to perform it.
It says in Dibrei Mordekhai that if the guests were all invited and it would be distressing for them if it were cancelled, or the hall was booked and there would be a substantial loss of money, in such a case, after the fact, one could be lenient and perform the Milah on Thursday or Friday. One must reiterate, however, that under no circumstances may a postponed Milah be held on Shabbath.
(See Sh. 'A., Yoreh De'ah, 262:2 and the Taz. ibid., 3. Y.D. 266:2. Rab Pe'alim, Yoreh De'ah, 4, 28. Dibrei Mordekhai, Lekh Lekha, Halakha)
Milah, Bris, Brit, Berith, Brit Milah, Postponed bris on Thursday or Friday