Leigh Griffiths has insisted that Celtic's invincibles tag has been well-earned this season, and has bristled at criticisms about the standard of the league.

The striker was irked by comments made by former Rangers striker Kris Boyd which appeared in a Sunday tabloid before yesterday's game against Hearts.

Griffiths netted thee opening goal as Celtic enjoyed a 2-0 win over Hearts to take them through the league campaign unbeaten, an achievement Griffiths was inclined to savour.

“I saw that from Kris Boyd this morning in his column," he said. "He said it’s the worst standard of Scottish football there has ever been. But if you look at it as a whole, Aberdeen have got a really good points tally, St. Johnstone are playing really well as are Partick Thistle. Rangers have had their ups and downs. But it is all about us and what we do. Going through the whole season unbeaten is quite an achievement regardless of what league you’re in.”

“Everybody is allowed an opinion. He played in a good Rangers team back in the day. We can only play what is put in front of us. It is a testament to the boys down there that we have faced different challenges throughout the season and come through it with the sun shining.”

Griffiths bagged his fourth title medal since being at Celtic yesterday and admitted that it felt a little special after the multitude of records which has been felled in the process.

“This one is a bit more special than others ones," he said. "Every title is great, but as long as we didn’t get beat we knew we were going to be invincible. That was the message going out at the start of the game. It is a great achievement for everybody at the club. We have now got one big push to go next week.

“After the first game against Lincoln Red Imps in the Champions League qualifier there were a few fans who weren’t nice to the boys, but the gaffer told us to be calm and stressed it was our first game as players. We knew we were going to be up against it at times, but credit to us. It shows what kind of mentality and character we have got in that dressing room downstairs."

For Griffiths, it was last Friday night when Celtic left Pittodrie on the back of a 3-1 win over Aberdeen when he first believed that the Invincibles ambition could become a reality.

Throughout the Celtic squad this season, the chance to reach that milestone has been played down and Rodgers maintained that it wasn't discussed until there was only one league game remaining.

“I think after the split was made we had two really tough trips, Ibrox and Pittodrie," said Griffiths. "I thought if we could get through them we had a really good chance. We started really well against Aberdeen, got the three goals early on and that was comfortable enough for us. After that game we really thought we could do it in the changing room.”