ANDY WALKER believes Celtic’s players stand on the verge of a ‘once-in-a-lifetime’ achievement by completing a treble-winning season domestically unbeaten.

Under Brendan Rodgers, the Premiership and Betfred Cup winners have now gone 40 games in Scotland without suffering the angst of defeat, bringing them to a mouth-watering meeting with Rangers in the William Hill Scottish Cup semi-final on Sunday.

Potentially just two more matches stand between Rodgers and a treble, while only five more Premiership games added to that would complete a campaign with a big fat zero in the losses column next to the Parkhead side.

Read more: Celtic big-game player Moussa Dembele 'has to' start against RangersGlasgow Times: 16/04/17 LADBROKES PREMIERSHIP. ROSS COUNTY V CELTIC. GLOBAL ENERGY STADIUM - DINGWALL. Celtic manager Brendan Rodgers at full time.

Walker was part of a Celtic side that went frighteningly close to achieving an unbeaten season. Back in 1995/96, Tommy Burns took his team to within four points of Premier Division winners Rangers on the back of season that saw just one defeat, which poetically came against their Ibrox foes. If that 2-0 win at Parkhead for Rangers had gone the other way, it would have been green and white ribbons around the trophy instead of red, white and blue.

Success and silverware has already been achieved 21 years on by the current class. But greatness, according to Walker, is now within reach.

“It’s their biggest game of the season of course because it’s the next game. There is a winner on the day and if you win it by whatever means the treble is still alive. And the fact Celtic would still remain unbeaten you are looking at a potential once in a lifetime experience for the players.

“I don’t know if anyone would come close to being involved again in a team that could go through a whole season undefeated. It really would be quite remarkable,” he said.

“I can remember being part of a team led by Tommy Burns and we only lost once all season and we still didn’t win the title. We pushed Rangers as hard as we could but they were better. Rangers players reacted to us improving and that’s what happens when you get rivals coming together.”

Walker admitted back in December that he didn’t believe such an unbeaten domestic campaign was possible. He is not the only one to have been surprised such a record is still on the cards.

Read more: Celtic big-game player Moussa Dembele 'has to' start against Rangers

In hindsight, it probably shouldn’t be too much of a shock. The bold Brendan could probably get a tune out of vuvuzela. As much as the likes of Aberdeen and Hearts have not managed to put up the same sort of fight as they did last season, or in the case of Rangers the challenge some of their own expected, the improvement of Celtic is by far greater than the diminishing qualities of their foes.

There is no melancholy among the masses now who have swelled inside Celtic Park. Just excitement about the state of their team right now.

Going forward, it’s clear that the resistance must come from a stronger Rangers. How Aberdeen can improve or get closer to the Premiership champions given their ever-contrasting budgets looks about as clear as pea soup, while the arrival of Pedro Caixinha has brought a breath of fresh air at Ibrox, if not a gust of crisp banknotes from the boardroom just yet.

However, even with an anticipated increase in challenge from across the city after the summer and even on Sunday, it’s hard to imagine Glasgow being anything other than green and white for the foreseeable based on what we have seen under Rodgers so far.

“It’s not a matter of me thinking it, It’s a fact Rangers haven’t been competitive for the title this year but realistically in the longer term they are the only ones to push Celtic,” said Walker.

“Looking the title Celtic have won over the last few years and they have stuttered and stumbled their way to it. Not this year. They’ve won this with a bit of style and there is a chance of this being a special season. To go through the entire season undefeated is a once-in-a-lifetime achievement. I don’t think it can be matched again.

“It’s still very much on. We are in the middle of April and we’ve been asking the question since November. They keep coming up with the answers.”

Read more: Celtic big-game player Moussa Dembele 'has to' start against Rangers

Beyond Celtic’s Scottish Cup campaign, whether that stops on Sunday or in May’s final, the attention will turn sharply to the Champions League qualifiers which will begin in the early days of July. Even though eventual qualification for the knockout stage will only add to Celtic’s wealth and therefore put them further out of the reach of their rivals, Walker insists it is still a positive for the Scottish game as it tries to rejuvenate itself.

“These games are so important to Celtic and Scottish football,” said Walker of the qualifiers. “They define your season.

“It’s up to Rangers and other to lift their game. If Celtic can drag them along and make them better I believe Scottish football will benefit from it.”

Sky Sports will show the Old Firm Cup semi-final and El Clasico exclusively live this Sunday.