Celtic face stiff competition from the Premier League and Bundesliga for centre-back Mark McKenzie, Philadelphia Union sporting director Ernst Tanner has told Sky Sports News.
The MLS side were in discussions with the Scottish champions in the summer for the USA international, but Celtic opted to sign Shane Duffy on loan from Brighton for a £2m fee.
Sky Sports News understands that Celtic are looking for another centre-back in January and McKenzie, 21, is high up on their list of targets again.
The Scottish Premiership side have been monitoring his situation for some time, but Tanner revealed they are not the only European club in the running to sign their prized asset.
Asked if there had been any further talks with the Glasgow club, Tanner said: "Not recently. Yeah there were and they signed other players. It's not necessarily going to be Celtic. There is a German league club and other European leagues going for that player. Some of the Premier League clubs are also observing him.
"We don't have any sort of pressure on him and he also doesn't need to force a transfer. He's a good player and plays in a competitive league.
"There is nothing on the table for him but I know there a lot of rumours out and we are certainly following that. There are some loose discussions at this moment but nothing concrete.
"The situation in Europe is pretty difficult due to Covid. Mark has certainly really stepped up over the course of the season and he is ready to go. But he could also stay here for another year or half-year."
'Poor recruitment to blame for Celtic slump'
Former Celtic midfielder Murdo MacLeod feels poor recruitment has been a major factor in their slump in form.
Manager Neil Lennon remains under intense pressure from supporters after Celtic slipped 13 points behind Scottish Premiership leaders Rangers on Sunday.
Celtic followed three consecutive defeats with a home draw against St Johnstone and have only taken six points from their last five league games.
MacLeod believes players must share the blame with Lennon for the dramatic reversal in fortunes - which has seen them win just twice in 12 matches - but he also questioned the summer signings.
Left-back Diego Laxalt has settled in well but goalkeeper Vasilis Barkas has been in and out of the team, defender Duffy has struggled and has been out of the starting line-up for six games, 21-year-old midfielder David Turnbull has only started once and striker Albian Ajeti has not scored since September.
MacLeod, who played for Celtic for nine years, told Sky Sports News: "Neil is the one that's been getting all the stick, but the players have got to look at themselves - every single one of them - and just look in the mirror: 'What am I not doing that I used to do last season?'
"Even a lot of the new players, because I always felt when you are bringing new players into the club, they have got to be better than the players that's already at the club. And I think this season, that's not happened."