Man Utd finally registered their first home win in the Premier League when they played the Baggies.
Leboeuf says Man United's performance against Baggies shows they are not a team that can compete at the top.
Frank Leboeuf was baffled by Anthony Martial's display in Manchester United's 1-0 victory over West Bromwich Albion on Saturday.
The ex-Chelsea star says Martial performances of late have left him a little bit "worried".
The 24-year-old Frenchman hasn't found the net in five Premier League games this season and continues to miss chances in key moments for United.
He had the opportunity to break the deadlock when Ole Gunnar Solskjaer's side hosted the Baggies over the weekend but wasted the chance once again and now there are growing calls for former PSG and Napoli striker Edinson Cavani to replace him in the no.9 position.
However, Leboeuf didn't waste time to call out his compatriot when speaking on the ESPN FC podcast about United's display, adding that the Red Devils were really below par over the weekend.
"I’m worried about Anthony Martial. He is a fantastic player and when he’s confident, he is okay," the former Chelsea defender said.
"He played with the international team and missed three chances against Portugal. He missed another chance today. For a world-class player, it was an easy chance.
"He has to be a killer. I’m not pleased with any of those players. What I saw was a poor performance.
"Even West Brom could have scored two goals. It’s not a team who can compete at the top if they perform like that against West Brom. It has to be better – this is Manchester United."