BBC
Former striker John Hartson believes Celtic do not have what it takes to make up a 10-point gap on Rangers at the top of the Scottish Premier League.
"I feel that Celtic are not good enough to go on an unbeaten run. Their defence is too leaky; they concede far too many goals," he told BBC Scotland.
"If Celtic were going to get back into this race, they'd have done it by now.
"There are still two Old Firm games, there are plenty of points to play for, but I think they'll drop more points."
Hartson, 34, played under Mowbray at West Brom after a successful five-year career at Celtic, which began in 2001.
But the former Welsh international feels it is too late for his old manager at the Hawthorns to turn things around in his first season at Celtic Park.
"Anything is possible. Celtic could get on a good run and Rangers could get on a bad run," said Hartson.
"But Rangers have their eye on the ball. They know what to do. They beat a very good Hibs team convincingly."
Speaking on BBC Radio Scotland's Sportsound programme, Hartson added that Celtic had blown the chance to keep in touch with Rangers in the race for the title.
He said: "Celtic have had several opportunities - Dundee United away from home, 1-0 up, you lose 2-1; Hibs, 1-0 up at home, you lose 2-1; the defeat away to Kilmarnock; the home game against Rangers where you are 1-0 up and you draw the game 1-1.
"It's too late this season; it's gone. The European campaign was gone early, they have gone out of the League Cup and now they are 10 points behind in the league.
"They couldn't hold on to a lead at Aberdeen and put pressure on Rangers going in against Hibs.
"It will take a massive effort now from Celtic to take this lead off Rangers."
Rangers and Celtic each have 13 games left to play, with the Ibrox side's lead augmented by a goal difference 21 better than their old rivals'.
If Celtic can win their remaining league matches, taking six points off Rangers in the run-in, they would still require Walter Smith's men to drop another four or, given Rangers' superior goal difference, five points to win the SPL.
Rangers have lost only one match in the current league campaign, and Celtic's longest run of consecutive SPL wins stands at three games.
For Hartson, a prolific scorer in his time at Celtic, the problems for the team are obvious.
"Although Tony has strengthened the front line with two very good signings in (Diomansy) Kamara and (Robbie) Keane, I don't think he has done anything in terms of his defence," he stated.
"They are leaking far too many goals, they are not tight enough, they are not brave enough to put their head through the ball.
"He had the same problems at West Brom and ultimately it led to his downfall."
And he added: "(Gary) Caldwell and (Stephen) McManus weren't everybody's cup of tea but they won three titles out of four under Gordon (Strachan) and they were stalwarts in that Celtic defence.
"He got rid of them and also got rid of (Danny) Fox at left back.
"When you play five-a-sides in training, you can have five strikers and five defenders against each other. The defenders will win all day long. You need people who really want to defend.
Hartson clutches the SPL trophy he won with Celtic in 2006
"The only one who really wants to compete in the air is (Glenn) Loovens."
With Rangers dropping two points at Motherwell last week, Celtic could have cut the gap at the top to five points before Rangers played Hibs on Sunday, but they were unable to hold on to a 4-2 lead at Pittodrie.
"They are a terrific side going forward; it's just defensively," continued Hartson on Celtic's problems.
"It's soul destroying when you've got the goals that have given you the lead and you can see the defence letting in goals willy-nilly.
"You go forward as a team and you defend as a team."
And Hartson highlighted one area where Rangers have a clear advantage over his former club.
"You need leaders. I saw Darren O'Dea wearing the captain's armband the other day, which baffled me," he said.
"Leaders are important, but if you have someone like Davie Weir, doing a fantastic job for Rangers, it helps you as a manager."
I can't disagree with BBJ.
We are in a pickle re: the SPL title and the defending is shocking at times.
