The 26-year-old had a ‘contract wrangle’ with the Bhoys last summer and has an uncertain future a year later due to interest in his signature.
Celtic convinced Armstrong to reject interest from other clubs to sign a new two-year deal at Parkhead, but the Scotland international is expected to be the subject of more speculation due to his fine form since returning from injury.
His contract expires in less than 18 months, meaning Brendan Rodgers has a decision to make whether to cash in or risking losing him for free next summer.
Signed from Dundee in 2015, Armstrong has gone on to make over 130 appearances in all competitions, scoring and creating 51 goals.
The 26-year-old has made 36 appearances for Celtic this season, contributing 10 goals, and could be tempted to move away from Parkhead.
Rodgers has made it clear how important he regards the midfielder given how much work went into agreeing a contract extension, so it’s likely that Celtic would reject any bids for Armstrong.