The Parkhead club only found out on Friday afternoon that the defender had to sit out the match as a punish-ment for receiving a red card in the pre-season friendly against Ajax in Amsterdam on July 21.
Scotland's Player of the Year was sent off by Dutch ref Bas Nijhuis for deliberately using a hand to stop a shot from crossing the goal-line.
Celtic made enquiries before leaving Holland the following day to establish if the red card would be reported to SFA, and were assured this would not be happening because it was such a minor offence, and not serious foul play.
However, on Friday, the Dutch FA decided to inform the SFA of the offence, and an automatic ban for the first competitive domestic game kicked in.
Lennon was astonished when the SFA – whose list of suspensions was issued to all clubs on Thursday without Mulgrew's name being included – got in touch with Celtic to tell them the player must serve the ban in the match against Aberdeen – less than 24 hours later.
By that time, Celtic had completed their prepara-tions for the match, including their set-piece drills, with the defender heavily involved.
Lennon accepts that the SFA were not at fault for the eleventh-hour decision to ban the player.
He said: "To be fair to the SFA, they did not receive any notification from the Dutch FA until Friday afternoon, so I attach no blame to the SFA on that one at all.
"We were under the impression that the referee was not going to report it and that it would have been waved away.
"That's what we were told after the game against Ajax.
"But, then, after having done our preparations for the game against Aberdeen, on Friday afternoon we were told Charlie was suspended."