Said Chris Coleman to the club website "Leon has suffered a small problem with his medial ligament and he'll be out for between three and five weeks.
It's a big blow for us because Leon has been looking very good during pre-season. He's been showing his best form since I have been at the Club so we will miss him.
Best against FC Brasov
"We will have to give him enough time to get over the problem but I have no doubt that Leon will be back as soon as he possibly can."