Martins missed four recent qualifiers for both the 2010 CAF Africa Cup of Nations and the FIFA World Cup, claiming he was nursing an ankle injury.
"We have to be careful about the issue of Martins because he is a good player even though no one is indispensable. However, we cannot force anyone to play for Nigeria, rather we prefer to work with willing players," said Amodu.
"He called me to say he was injured. I insisted that he should still join us for our friendly in Austria in May but he did not comply. I want to take him at his word but at the same time, I'm watching him."
Amodu also defended his team's performance in the qualifiers.
Fans were not impressed by the Super Eagles despite recording a 100 percent record after four rounds of matches.
Nigeria lead a group that includes FIFA World Cup hosts South Africa, Sierra Leone and Equatorial Guinea with a maximum 12 points.
"We inherited a team that was in tatters, a team that needed to regain its confidence. We have achieved some results but we are not there yet. You're never satisfied if you an ambitious person like me because you keep asking for more," said the coach.
"We are making progress. I have been satisfied with the conduct of the players as well as their commitment."