Pickford won his third international cap in Saturday's 2-1 win over Nigeria, playing the full 90 minutes, and Martyn feels that the custodian selected to play in Thursday's friendly against Costa Rica is likely to start England's campaign in Russia.
"A really difficult decision isn't it? I think it's between [Pickford] and Jack Butland really who gets the nod," the former Crystal Palace and Leeds United goalkeeper told Sky Sports News.
"Jordan had a really great season with Everton and was probably the shining light for them.
"I think Jack Butland is a very capable goalkeeper as well. Those two are probably the frontrunners.
"Whoever gets to start in the next game might be the one that gets the nod for the first game during the World Cup."