Celtic are one win away from a seventh successive Premiership title, 13 points clear of their Glasgow rivals, and can clinch it against Hibernian at Easter Road on Saturday.

Both Rangers and Celtic have achieved nine titles in a row in the past but Brendan Rodgers' Celtic, currently looking unstoppable in Scottish football, beat Celtic 4-0 in the Scottish Cup semifinal.

However, Johnston told Press Association Sport: "I don't think anything is inevitable in football. I don't think that [10 in a row] is inevitable at all.

"If you look at football, it has its ups and downs. How do you think Manchester United fans feel now, being 13 points or whatever behind their city rivals?

"These things are going to happen. That's why football is so engaging -- there is nothing predictable about it.

"When you can upset predictability that is what is exciting about it, and hopefully we have many more chances to do it."

Meanwhile, Johnston said Rangers were "ahead of the curve" in their recovery.

The club were sent into the bottom tier of Scottish football in 2012 after a financial implosion but are now in their second season back in the Premiership.

"We are probably doing a little better than we would have imagined back in the dark days of running out at Brechin in the fourth tier," Johnston said.

"In terms of looking forward from where we were four or five years ago at the bottom, the progress that has been gradually made, we are probably ahead of the curve in reality if we finish second or third.

"We are making progress. Hopefully the curve will be fast but it is still going to be gradual -- it is not going to happen overnight."