Armstrong joined Celtic from Dundee United in February 2015 and has a contract until June 2018.
The 23-year-old arrived at Celtic Park with a strong reputation, but he has struggled to play well this season.
The former Scotland Under-21 international is not guaranteed a regular place in the Celtic starting lineup at the moment.
Former Celtic midfielder and manager Hay has given his opinion on Armstrong’s current situation at the Scottish Premiership giants, suggesting that he is struggling because he is being played out of position.
“Stuart Armstrong has looked increasingly uncomfortable playing out of the left and although he was obviously happy when he first arrived at the club simply to go out and try to make an impression, you can see now that he is struggling to find his best form there,” Hay wrote in The Glasgow Evening Times.
Celtic have the strongest squad in the Scottish Premiership, but they are not doing too well at the moment. Ronny Deila’s side are currently just four points clear at the top of the league table.
Second-placed Aberdeen are hot on the heels of the Glasgow giants, who are in danger of losing the Scottish Premiership title this season.