The ex-Toffees man suggests that his former club are underachieving.
The Toffees sit 12th in England's top flight in what has been a season littered with inconsistency from Martinez's side, who have won nine of their 28 league outings.
Their position might surprise some given the talent available to the Spaniard, who has the likes of Romelu Lukaku, Aaron Lennon, Kevin Mirallas, Ross Barkley, Gerard Deulofeu, John Stones and Seamus Coleman in his squad.
It has certainly surprised Gray, who claims that Everton, on their day, are a threat, but believes that the former Wigan Athletic boss is majorly underachieving on Merseyside this season.
"Everton, on their day, are as good as anything I think," he said on beIN Sports.
"The problem he [Martinez] has is, nine league wins out of 28 games is, in my opinion as an Evertonian, and with the quality of footballers he has at his disposal, is poor."
Everton find themselves with very little to play for in the Premier League as Martinez and co sit 13 points clear of relegation, but 11 shy of fifth-placed West Ham United in the Europa League spot.
That is why this evening's FA Cup quarter-final with Chelsea at Goodison Park is so important. Should they lose, it would effectively end their season and heap more pressure on Martinez in the process.