This means that the 24-year-old Scotland international winger could leave Celtic Park at the end of the season.
Former Celtic star Miller does not believe that the Bhoys will miss Forrest if he does depart in the summer.
“It used to be if you didn’t sign a deal you didn’t play," Miller told The Daily Record. "I’m not sure it will matter if Forrest’s frozen out for the rest of the season - he’s not playing anyway.
“I’m not sure people would notice to be honest. If you asked most Celtic fans, there wouldn’t be many tears if he left, which is a shame.”
The question is where Forrest will go if he leaves Celtic at the end of the season? Premier League? Championship?
“There’s good money in the Championship but whether there will be clubs at that level queuing up for him now, I don’t know,” said Miller. “There was a lot of interest in him a couple of years back but he has suffered a lot of injuries since then.
“The question is where is he going to go. Signing him would be a gamble for any club because of his injury record in recent years.”
According to The Daily Mail, Premier League side Norwich City and Championship outfit Queens Park Rangers are interested in signing Forrest in the summer transfer window.
Celtic are at the top of the Scottish Premiership table at the moment with 61 points from 26 matches.
The Glasgow giants are six points clear of Aberdeen, who are currently second in the standings.
The Bhoys will return to action on Friday evening when they take on Hamilton Academical away from home at New Douglas Park.