Seventeen were at Parkhead while Tottenham sent representatives to the Allianz Arena a fortnight ago to watch Tierney and Manchester United have been keeping tabs on him through most of 2017.
Left-back Kieran Tierney, 20, and striker Moussa Dembele, 21, are pivotal members of the Celtic squad and won’t be sold without considerable resistance. Tierney recently signed a six-year deal to keep him at Parkhead until 2023.
Dembele signed for Celtic in summer 2016 with the Glaswegians fending off considerable interest from the Premier League, notably Arsenal, when the signed him from Fulham.
Manchester United are keen to sign Scottish international Tierney with manager Jose Mourinho short of faith and patience with Luke Shaw. The 22-year-old is a target for Southampton with the Portuguese expected to sell him next summer.
Dembele, with 37 goals in his 55 Celtic appearances, continued his prolific club form of last season into this campaign, as well as for France Under-21s for whom he has scored four times in his eight caps.
Didier Deschamps named the 21-year-old striker in his provisional squad for the upcoming friendlies against Germany and Wales.
Celtic remain unbeaten in the Premiership and face Motherwell in the Scottish League Cup final at the end of November, a run which currently extends to 62 games.