And that will leave Liverpool boss Jurgen Klopp guessing as to whether the Manchester City pair could yet play some part in Sunday's huge Premier League showdown at Anfield.
City insiders stated De Bruyne, who has been absent for two months, showed no apparent issues with the knee ligament injury which has robbed Pep Guardiola of his star man at the start of this campaign.
The Belgium midfielder was seen running and shooting, although City's medical staff are keeping a tight lid on where the 27-year-old presently stands.
Left-back Mendy is also knocking on the first team door again, having recently been ordered by Guardiola to stay away from the training ground after turning up late for a rehab session on his injured foot.
The availability again of the France international would certainly be a huge boost to the Premier League champions, who do expect to be without injured back-up Fabian Delph, this weekend, although Oleksandr Zinchenko is also able to deputise and was rested for Tuesday's late Champions League win at Hoffenheim.