Tierney has starred for club and country since breaking through at Celtic in 2015-16, winning four international caps and claiming back-to-back PFA Scotland Young Player of the Year Awards.
The 20-year-old left-back has been earmarked as a future Celtic captain and recently wore the armband in a Scottish League Cup win over Kilmarnock, showcasing his versatility with an impressive performance in central defence.
Adam, capped 26 times by Scotland, insists it is only a matter of time until his countryman makes a move to one of England's top clubs.
"Tierney is Scotland’s best player now – he is different to anything else we have got," Adam told the Daily Record.
"His hunger, desire and quality make him the best we have produced for years.
"Brendan Rodgers has done a great job with him at Celtic and the fact he loves the club is a bonus."
Celtic manager Rodgers has previously voiced his confidence that Tierney will remain at Parkhead for the foreseeable future.
"He’s a Celtic player with another four years on his contract," the former Liverpool boss said in May.
"He absolutely loves it here but I would expect the very biggest clubs in the most competitive leagues to be interested in him because he's a huge talent."