Gordon Strachan has suggested that two of his former clubs could have struck a deal which has backfired.
Southampton signed Armstrong for £7 million, after three seasons at Celtic.
The 26-year-old has found it tough to make an impression at Southampton so far.
He has started only one game for the Saints, and come off the bench three times, for a combined 101 minutes of Premier League football.
Celtic have also been struggling for form, and Strachan believes both parties have been regretting the move.
He told Paddy Power: "At this moment in time, Celtic’s flair players aren’t on form, so they need to find another way.
"Which shows how they’re missing Stuart Armstrong. His runs could push a defence back another eight or ten yards. At the same time, shouldn’t he be missing Celtic, too?"
Armstrong followed a well trodden path with his move from Celtic to Southampton.
Fraser Forster, Victor Wanyama and Virgil van Dijk have all enjoyed success with the same route, and Armstrong will still fancy his chances of long term success.
The biggest concern is that Celtic have been alleged to be missing him.
It wasn't seen as a huge worry at the time, and so it encapsulates their troublesome form this season that it is even a talking point.
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