Coutinho, 26, has lost his place in Valverde's starting XI this season after a string of poor performances in LaLiga.
This has led the £142m record signing to be linked with a move back to the Premier League - while reports in England suggest he'll be used as make-weight for Neymar's potential return.
The Brazil international netted Barca's only goal in a 2-1 defeat away to Levante on Thursday but delivered an overall poor performance - much to the frustration of the Blaugrana coaching staff.
And Valverde has now called for the former Liverpool superstar to take heed from one of his teammates who's now kept him out the starting XI.
"When I wasn't playing Dembele everyone asked about him," Valverde said after the game, as per Marca.
"Now he plays and Coutinho doesn't and it is the other way around. Coutinho has to work to turn things around.
"He is not happy, but has to fight."
Coutinho has scored six goals and registered four assists in 24 games across all competitions this season.