The Scotsman was set to start against West Ham but was pulled from the XI before a ball had been kicked.
During the pre-match warm-up, Tierney felt something and immediately left the field.
In his place, Sead Kolasniac came in but it did not have a detrimental effect on the result.
Arsenal emerged 2-1 winners after a late goal from Eddie Nketiah to make it two wins out of two.
But fans were concerned with the state of Tierney, who had an injury-ravaged season last year and there are fears history is repeating itself.
However, Arteta has moved to quell those fears after insisting that the ex-Celtic star is all good.
He said: “Kieran is fine. He had a little muscular discomfort in the last few days.
“He tried today and worked in the warm-up but he wasn’t feeling comfortable today.
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“We believed that he was going to be fit but during the warm-up, in the last 10 minutes, he said he wasn’t feeling OK.
“We had to make a decision. We were prepared just in case and Kola came on and had a good game.”
The Gunners initially took the lead through Alexandre Lacazette before Michail Antonio equalised on the cusp of half-time.
Though they lacked the same fervour they played with against Fulham, Arsenal still left the match with all three points.
With five minutes to go, Nketiah grabbed the winner and Arteta was over the moon.
“What I like is the approach the boys had in the last 25 minutes where I could see they were a bit down and then they lift it,” Arteta said.
“Probably a few months ago we would have drawn or lost that game and today we win it.
“In the end you have to find a way because there will be games like this through the season.”