The Chelsea star was influential in his side's 4-0 round-of-16 win over Hungary on Sunday, scoring the third with a spectacular strike.
However, having picked up a knock in that game and subsequently being substituted, he joined Thomas Vermaelen in missing out on Belgium's latest training session.
Wilmots, though, is optimistic his captain will recover in time for the last-eight meeting with the Welsh.
"Hazard felt a kind of thigh contraction at half-time against Hungary, that's why I replaced him in the second half," he said.
"I think he will be back in training on Thursday. He is in the care of the physios and is working with them.
"He is recovering well enough that he should be 100 per cent the day before the match."
Belgium lost their opening game of Euro 2016 to Italy, but have been in fine form since, winning all three games without conceding and scoring eight goals in the process.