Nigeria manager Shaibu Amodu has warned striker Obafemi Martins that he needs to improve his physical and psychological fitness.
Newcastle star Martins has struggled with injuries over the past year and he has not represented his country since Amodu took charge in April.
The 24-year-old has returned to Newcastle's first team over recent matches, scoring three goals in his last three outings, but Amodu still expects improvements.
Nigeria play Colombia in a friendly on Wednesday and in preparation for that match Amodu watched Martins against Fulham last weekend, but he was not impressed.
He said in The Sun: "Martins needs a look at his psyche. I am worried about him.
"Obviously he's a good player but he needs to be prepared mentally to take up the challenges.
"His team have found themselves in a precarious situation and I think psychologically now he should be worried himself.
"I haven't had the opportunity to work with Martins closely because since I came back to the national team he has not been able to show up.
"His excuses have been injury but I think he is injury-prone. He needs to work more on his fitness.
"He's small in physique and plays in attack so he is prone to knocks.
"The only way you can keep playing at that level is to be very, very fit and to stay away from all the social vices.
"I'm not saying that is what's involved but it is a clear criteria if you want to stay at the top of your game all the time."