Celtic are monitoring Philadelphia Union centre-back Mark McKenzie.
Sky Sports News understands the Scottish champions have asked to be kept informed on any developments regarding the 21-year-old, who is keen on a move to Europe.
McKenzie became a USA international when he made his senior debut in a friendly against Costa Rica in February.
Celtic's priority in the current transfer window is now to sign a left-back, but it's believed they would like to bolster their central defensive options, as well as adding a winger.
Last week, Sky Sports News reported that representatives of centre-back Kristoffer Ajer had asked the club for a valuation of their client, ahead of a potential move away from Parkhead.
The summer transfer window will run for 10 weeks from July 27 and close at 11pm on October 5.
A domestic-only window for trades between the Premier League and EFL then runs from October 5 and closes on Friday, October 16 at 5pm. Follow all the news and analysis on Sky Sports News and across Sky Sports' digital platforms, including with our dedicated Transfer Centre blog.