The 25-year-old has long been linked with a move away from Villa Park and speculation over his future is rife as the summer transfer window approaches.
The England international has been out of action since February through injury but had been enjoying a superb season for Villa, scoring six goals in his 22 Premier League appearances so far this campaign.
Manchester United have been interested in the midfielder for some time, with Manchester City and Liverpool also linked with Grealish, while Tottenham came close to signing him in the past.
The Red Devils were thought to be leading the chase for his signature, but Barnett says otherwise, warning United that they must act if they do indeed want Grealish this summer.
‘The truth is we don’t know [what will happen],’ Barnett told SNTV . ‘There are many clubs [interested] and I wouldn’t put Manchester United at the top of that [list].
‘But he could stay. He could stay as well so it’s a conversation the club, Aston Villa, will have with Jack and ourselves then we’ll see where we go.
Grealish is under contract with Villa until 2025 and will be hoping to play a big role for England at the European Championships this summer.
Barnett insists the player’s thoughts are not on a potential move, although if he is to star for England in the Euros, speculation will only mount further.
‘He loves Villa, but I think we just have to wait to see how things pan out,’ Barnett told Sky Sports.
‘At the moment he is a Villa player and he has had no thoughts about anything else. We have to do what is best for Jack and for everybody else.
‘I think he is a very special player. I think he maybe should have been playing for England a little earlier.
‘It is unfortunate that he has got this injury at the moment but that will be fine. He has got a great mentality.
‘On the field, he knows exactly what he wants to do, how to do it. I think he could be a big star in the summer. Only hope that he is given a chance and that will be great.’
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