Kolasinac, who is naturally a left-back, was a shock inclusion as a left-sided centre-back in a back-three against the reigning champions.
Mikel Arteta's makeshift defence was exploited by City, who ran out 5-0 winners at the Etihad.
The selection of Kolasinac stunned many Arsenal fans as it was assumed the 28-year-old would be sold this summer, following his loan spell with Schalke last season.
According to Winterburn, who spent nine years with the Gunners, Kolasinac was indeed halfway out of the Emirates shortly before playing against City.
Asked by TribalFootball.com, on behalf of BuzzBingo, why he thought Kolasinac started, Winterburn said: "I was surprised, I heard the day before he was terminating his contract, so to see him in the line up was a surprise.
"Arsenal went with a back three, so it didn't surprise me in that sense because there's a few players out.
"If you looked at the system it wasn't really a shock because of who was available.
"But, this is a player who was out on loan and looked for all the world like he was leaving and suddenly he pops up in the team.
"Arsenal just need to reset and restart the season again, hopefully we get a fully fit squad so there's no doubts and the judgement will come."
Any chance of Kolasinac leaving the club this summer could be over after he suffered an ankle injury in Bosnia and Herzegovina's draw with France.
Turkish clubs had shown interest in the former Schalke man, with their transfer deadline open until September 5th.
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