Arsenal manager Mikel Arteta's mood at going top of the Premier League was soured on Saturday by another injury setback for captain Martin Odegaard in a 2-0 win over West Ham.
The Norwegian set an unwanted record by becoming the first player in Premier League history to be substituted before half-time in three consecutive starts.
Odegaard also came off in victories against Leeds and Nottingham Forest due to a shoulder problem.
The 26-year-old appeared over that after his eye-catching display in the Gunners' 2-0 Champions League win over Olympiacos in midweek.
But he had to be withdrawn again on the half-hour mark at the Emirates after colliding knees with West Ham's Crysencio Summerville.
"I think he had a clash, knee-to-knee, and immediately he was uncomfortable. I just spoke to him and he is not positive about it," said Arteta, who revealed Odegaard was in a knee brace after the match.
"We have to wait and see the extent of the injury. We will have to find solutions, but obviously, he is our captain and is a player who gives us a completely different dimension with things that he can do, especially in the attack.
"Let's wait and hopefully it is not that bad."
Otherwise, Arteta was able to enjoy his 300th match in charge as Arsenal moved a point clear of Liverpool, who lost for the third consecutive game at Chelsea.
"I want to thank everybody, especially my coaching staff who have been with me since day one and without them it's impossible, first of all, to do the job and secondly to enjoy it," added Arteta.
"I wanted to celebrate it with a win, I've got it. Now we have an international break to enjoy it and use the time as well to prepare because what's coming in the next break is going to be really difficult again."
