Janssen has made 32 appearances for Spurs this season but has not been deemed worthy of a starting berth for almost two months.
The Dutchman started January's FA Cup victory over Aston Villa but has had to make do with sporadic substitute appearances in the weeks that have followed as Kane has hit top form in front of goal.
Janssen was brought on in the latter stages of Sunday's hardfought 3-2 victory over Everton, winning the free-kick which led to Dele Alli's late goal.
And Kane is adamant the 22-year-old must continue to give his all during the run-in as Spurs attempt to catch Premier League pacesetters Chelsea.
"He's just got to do what he did against Everton, even though it might have only been three or four minutes at the end," Kane told Press Association.
"He held the ball up, won free-kicks and saw the game out for us and that's what he's got to do every time he gets an opportunity.
"He has to try to impress no matter how many minutes it is. I was the same, I tried to do as much as I could in that time.
"He's important, we are a team, we are a squad, every man is important," Kane insisted.
Janssen has scored five goals for the north Londoners but is yet to find the net from open play.
The striker said earlier this month that he has given himself a year to succeed at White Hart Lane and is refusing to throw in the towel as the self-imposed deadline approaches.