The former Tottenham defender was pleased with the performance of Janssen against Southampton at White Hart Lane on Sunday.
The 22-year-old Netherlands international striker did not start the match, but he came on as a substitute in the 86th minute.
Roberts was following the game, and he was pleased with Janssen’s cameo appearance.
@vincentjanssen done very well for that last ten mins important cameo— Graham Roberts (@GrahamRoberts4) March 19, 2017
Janssen has struggled to play well for Tottenham this season and has not contributed much to the team.
Even with Harry Kane out injured, the Dutchman cannot get a start - he has been that disappointing.
Roberts’ encouraging message, though, should boost the confidence of the 22-year-old, who is talented and has a lot of potential.
Tottenham won the match 2-1 against Southampton, thanks to goals from Christian Eriksen and Dele Alli.
Spurs are second in the Premier League table at the moment with 59 points from 28 matches, 10 points behind leaders and London rivals Chelsea.