The former Celtic midfielder and manager has also observed that Dembele looked short of pace against Bayern Munich at Celtic Park in the Champions League this week.
The 21-year-old France Under-21 international started the match on Tuesday evening and played for the entire 90 minutes, as Bayern won 2-1.
Hay has suggested that the former Fulham youngster is lacking match fitness at the moment.
Writing in The Glasgow Evening Times ahead of Celtic’s Scottish Premiership match against St. Johnstone this afternoon, Hay observed: “I’ll be curious to see where Leigh Griffiths gets the nod to start or whether it is Moussa Dembele.
“I think the Frenchman looked short of the pace on Tuesday night and I just wonder of he needs to get his full match sharpness back.”
Dembele is one of the best strikers in the Scottish Premiership, but the youngster has only just returned from injury.
The Frenchman was one of the best players for the Hoops last season, and he will soon return to his best.
Leigh Griffiths has made the most of the chances he has got in the absence of Dembele, and the Scotland international striker is playing well at the moment.
Celtic are the best team in the Scotland, and they should be able to pick up all three points from their away game against St. Johnstone in the Scottish Premiership this afternoon.