Former Celtic ace Vidar Riseth has warned Kris Ajer he needs to be much 'stronger' if he wants to attract interest from top clubs.
The defender has been widely linked with a move to AC Milan in previous windows and speculation will no doubt grow again in January.
Ajer's performances haven't been at the same level this season, however, as Neil Lennon's side continue to leak goals at the back.
And compatriot Riseth reckons the Norwegian needs to show that form once again if he has any aspirations of making the switch to a club like Milan.
He told The National: "I still watch a lot of games because I consider myself a Celtic fan and I am not happy with Kristoffer right now.
If you are talking about clubs like Milan looking at you, then you need to be much stronger – in the head and on the pitch."
Ajer has 18 months left on his current deal with the Premiership champions, but he has yet to sign an extension.
The Parkhead club could look to cash in on the centre-half in 2021 if a suitable offer is on the table.
