Egan was injured in a first-half challenge with Blues' £30m forward Beto. He soldiered on only to make way midway through the second half.
The centre-half is due to now link up with the Republic of Ireland on international duty. They visit France in a European Championship qualifier on Thursday and host the Netherlands on Sunday.
It remains to be seen if Egan features, with the Blades management no doubt mindful of his condition ahead of their resumption after the first international break of the campaign.
Heckingbottom said: “We can’t stop them from going away. If Ireland want to see and assess him then they will. If he’s not fit, he doesn’t play and if he is, then he’ll play."
Heckingbottom revealed that Yasser Larouchi also came off with an injury issue in the game against the Toffees.
The Blades chief added: "Generally when it’s a bang, you hope that they’ll run it off in a couple of days. "Egs was knee and ankle but he didn’t feel his knee in the second half, he would have carried on, but I could see it was affecting him and it was my call really.
"When you’ve got Bash (Chris Basham) to come on and move Anel (Ahmedhodzic) inside, we’re not weakening at all. So it was the sensible thing to do.”