"He never told us he had an injury but played one or two games with it and we had to keep taking him off.
"We think he did it four or five weeks ago, maybe on an international break, but the worry is it hasn't gone away.
"We are safeguarding Ruud at the moment.
"He has had this niggle at the bottom of his calf and it is one of those things that we need to get rid of now, otherwise it will keep resurfacing.
"If you don't get to the root of the problem and clear it up completely it can keep resurfacing - as has happened with Ruud.
"We've got to be dead sure he is 100%.
"You worry about how long he is going to last in games. You are wondering when you can take him off and if it is a tight game, you don't want to take him off at all.
"We will monitor his progress over the weekend before we decide whether he will play on Monday."