Hartson confirmed Tottenham wide man Bale and Celtic defender Matthews - neither of whom had taken part in the Dragons' training session on Tuesday - were nursing heel and ankle problems respectively, but stressed the pair are expected to be available for the Group A clash with the Scots at Cardiff City Stadium.
"Gareth Bale came down to the training ground today and worked with the physio," Hartson said.
"We feel he will be okay for Friday. It was just a case of getting him ready.
"Adam Matthews did the same as Gareth, but we feel they will both be fine."
Hartson also revealed Celtic midfielder Joe Ledley, a third player not to feature in yesterday's session, had taken part in full training on Wednesday.