Henrikh Mkhitaryan says he is "not sure yet" if he will be fit for the Manchester derby this weekend.
The midfielder, who made a £26m move from Borussia Dortmund to Manchester United in July, missed Armenia's World Cup qualifier against Denmark on Sunday night with a thigh injury.
Mkhitaryan underwent a scan on the problem, which was sustained in an off-the-ball collision with Marek Suchy during the first half of Armenia's friendly with the Czech Republic last Wednesday, and was expected to be out for around 10 days.
In a post on Instagram, he confirmed he is a major doubt for Saturday's game against Manchester City, live on Sky Sports 1.
"I continue extensively my rehabilitation, but I'm not sure yet if I will be fit for the derby this weekend," he said.
"I'm motivated as ever and plan to put all my energy to be in great shape as soon as possible... A simple devotion to what I love most - football!
"Thanks for sending me your love and support."
Mkhitaryan has featured in all four of Manchester United's games so far this season, all of which have resulted in victories.