Barkley missed Everton's 2-0 win over Norwich City on Saturday after picking up a similar injury to the one which kept team-mate Leighton Baines for over a month earlier this season.
The England international will undergo scans on the problem and Martinez is concerned about how long Barkley could be missing for.
"We are a little bit worried," said Martinez. "We are going to assess him.
"It's a very similar incident to the one that Leighton Baines had. Before we say exactly what it is there will be more scans, but it could be a fracture in his toe.
"Knowing Ross, he is a young man, hopefully he is going to accelerate the (recovery) process."
Spectacular strikes from Gareth Barry and Kevin Mirallas against Norwich lifted Everton back into the top four and Martinez believes his side put in a complete display on home soil.
He said: "I thought it was going to be a very difficult game, and it proved to be. From the beginning, they played with two strikers to try and hit us on the counter and I felt we dealt with that really well.
"The amount of opportunities that we had, if we had that clinical touch in front of goal, it would have been the difference. But we are very pleased.
"Norwich had a proper go in the second half but we defended well and kept a very important clean sheet.
"In this type of game you can lose your concentration. I thought we controlled the game very well and got three well deserved points."
Martinez is delighted with how Everton's season is shaping up, but insists he will not read too much into league tables until much later in the season.
Asked when he thinks things get serious, the Spaniard added: "The last nine games. In the league, I like to work towards the final third of the season.
"The last nine games of the season, that is when you get that real significance of every point and an idea of where you are in the table and other results affect you. We are just trying to get as many points as we can.
"The last four games of the season at home are against the teams that we are fighting at the moment. We are trying to get better."