The 22-year-old signed for Forest on a season-long loan deal from Wolves in the summer, although he has failed to make any sort of impact thus far.
The Spanish striker has made just two league starts for the Reds, and has struggled to break into the team ahead of Lewis Grabban who has scored 10 goals in 20 games this term.
Having failed to find the back of the net in a total of 13 appearances for Forest, reports from Spain have recently linked Mir with a move away from the City Ground.
Speaking to Nottinghamshire Live, former Reds striker Birtles has insisted that it would be the right move for Mir to leave in January in order to make way for another striker.
He said: “While I do feel an element of sympathy for him and the way he’s struggled to make an impact, it’s now important to move him on in the January transfer window and free up some money in the budget.
“Mir would probably welcome a move away, to go somewhere he can try and play regularly and find his goalscoring touch, because with the greatest respect in the world, it doesn’t look like it will be forthcoming in Nottingham, and right now, time is not a commodity they can afford.
“Sabri Lamouchi needs a couple of players to come in and hit the ground running, to have an instant impact at the City Ground and take some of the pressure off Lewis Grabban.”
Can you get 15 out of 15 on this Forest quiz?
Forest are expected to sign another forward in the January transfer window to add depth up top, as Sabri Lamouchi’s side look to cement their place in the top six.
The Reds sit fifth in the Sky Bet Championship table, one point clear of seventh place with a game in hand.
It would undoubtedly be the best move for Forest to let Mir go back to Wolves in January.
Expectations were high when they first signed him, but his game time has been limited and he just hasn’t taken his chances when he’s started.
He doesn’t use his aerial threat and physical prowess to full effect and hasn’t come anywhere close to finding the net.
A move back to Spain could be best for him.