The initiative swung back to Rangers, who beat Hibernian 3-0 at Ibrox on Sunday to restore their 10-point lead over their Old Firm rivals at the top of the table with 13 games remaining.
Gemmell, who played left-back for the Celtic side which won the European Cup in 1967, said that there is now no margin for error at Parkhead.
"Celtic have put themselves in the position where they cannot drop any more points," he said.
"Every game is vital but they are starting to run out of them.
"They have to play Rangers twice and at the same time hope to win all their other games, but that is a big ask.
"The big disappointment for Celtic fans is that they are losing too many goals that could be prevented.
"That is not a sign of a championship-winning team.
"You've got to start with keeping the back door shut, build from the middle and then pop the goals in at the other end.
"If you look at any teams in any country who are looking to win their league, their goals-against record is usually excellent.
"If you don't lose goals then it is easier to win games.
"But Celtic know the situation they are in now."
Mowbray will be without defender Darren O'Dea for next week's game against Dundee United at Parkhead after the Irishman was sent off against the Dons for picking up two yellow cards.
With Glenn Loovens and Jos Hooiveld injured, 18-year-old Josh Thompson could be paired with 19-year-old Thomas Rogne at the heart of the defence.
Gemmell believes the Parkhead men will simply have to cope with the adversity.
He said: "It shouldn't be a worry for Tony Mowbray, he brought both players in and so he must have confidence in them.
"You will get injuries, suspensions and loss of form and you have to face up to it.
"All teams have the same problems in the run-in."
The Pittodrie fixture was shrouded in controversy when it was reported that Aberdeen boss Mark McGhee, a former Celtic striker and self-confessed Hoops' fan, was set to field a weakened team with one eye on the Scottish Cup replay on Tuesday against Raith Rovers.
An irate McGhee cancelled his regular pre-match press conference as a result of those reports, and after the game talked about the "scandalous" way in which his integrity had been questioned.
As it turned out McGhee kept the same starting eleven which had drawn 2-2 at Hibs and they were well worth the point.
The first half ended level after goals from Diomansy Kamara and Marc-Antoine Fortune had been cancelled out by Michael Paton and Darren Mackie.
The visitors went two clear with strikes from Robbie Keane and Aiden McGeady and the three points looked secure.
However, Aberdeen striker Steve MacLean reduced the deficit from the spot before grabbing a dramatic late equaliser as O'Dea was sent off in the final stages after picking up a second yellow for a foul on Dons midfielder Gary McDonald.
McGhee praised former Rangers youngster MacLean, whom he brought in on loan from Plymouth Argyle until the end of the season.
He said: "There was always a fear that we were going to lose Lee Miller, which we did, and I wanted somebody to link the play.
"In order to play the way I want my teams to play you need a centre forward that can bring other people in to play and he did that."