Belgium lost 1-0 in Cardiff, handing Wales a rare chance to qualify for a major international tournament, and Wilmots said he was disappointed with both of his strikers.
“We are a bit disappointed. The first half was good, but we’ve given away a goal and that made Wales stronger,” Wilmots told Belgium website Sporza.
“Nainggolan misjudged in this moment but he’s a good player. It is all too easy now to blame him.
“I changed my system afterwards, [bringing on Lukaku] because Benteke was isolated. I then played with two strikers, but they need more crosses.
“We asked them to get to the front post, but they stood there like two poles.
“We missed Marouane Fellaini in this game because this really was a match for him. He gets in the box.”