Tottenham head coach Mauricio Pochettino believes leading striker Harry Kane is being hampered by his face mask.
Kane has been forced to play with facial protection after breaking his nose in Tottenham's FA Cup defeat to Crystal Palace two weeks ago.
The 22-year-old has not scored in the three matches since suffering the injury, following Wednesday's 1-0 defeat at West Ham.
Pochettino fears the mask might be distracting the England international as second-placed Tottenham host fellow Premier League title hopefuls Arsenal on Saturday in one of the biggest north London derbies in recent memory.
"If you analyse all the strikers in the Premier League it's difficult to have 10 chances every game," Pochettino said. "At West Ham, Harry had two or three clear chances to score. Unlucky. Sometimes it happens.
"I have full confidence in him. Sometimes a period arrives when it's difficult to score. He is not a machine.
"Then he's playing with a mask. Sometimes it can disturb you - when you are creative.
"Maybe it's easier for [Chelsea defensive midfielder] Nemanja Matic or different players that play behind, because it's not their problem. But you need to be sharp when you are offensive and creative. Sometimes it can disturb you a little bit.
"He must wear the mask for a few weeks more, though, a minimum of three weeks.
"He is also still learning to deal with being a leader and the top scorer and one of the key players of Tottenham and the national team. It is not an easy job but we are happy in the way he developed his leadership."