Debuchy was released from his Arsenal contract last week and signed for ASSE as a free agent.
Dernis, now with AS Lattoise, said: "We all have little flaws. But Mathieu is still an international. The little catch presently may be his lack of playing time. He says he feels good physically but will need to play regularly to show his quality.
"I remember a guy who gave himself thoroughly. The fact that he played little in recent months can be detrimental to him. Now, with experience, I think he'll be able to handle it. What I wish him is to quickly glean the atmosphere there is to help the team to fight back, to fill the deficiencies of Sainté. Knowing him a little, I think he'll quickly blend into the team."