Manchester United striker Edinson Cavani has revealed the injury that kept him out of the defeat to Manchester City is a recurrence of tendon damage.
Cavani missed the 2-0 derby loss to the Premier League champions at Old Trafford on Saturday after scoring in the win at Tottenham and making a substitute appearance during the Champions League draw at Atalanta.
The striker was omitted from Uruguay's squad for World Cup qualifiers against Argentina and Bolivia following the setback.
Cavani says the injury is one he was also troubled by in pre-season but did not shed any light on how long he might be sidelined for.
The forward told El Observador: "The issue was like this. Before starting the season, I had discomfort in a tendon.
"It made me spend a couple of weeks out until I began to gain some minutes [on the pitch] in my team. I had to go back to the national team, always with a bit of pain, but with the hope that it would disappear. It was improving but, after Tottenham, it started coming back.
"They are difficult injuries and I decided to have the treatment so that it does not continue to get worse, and to recover as soon as possible to be fit for my team and the national team."
Cavani has only started two games for the Red Devils this season, coming off the bench six times and scoring just the one goal against Spurs.
Struggling United are next in action against Watford at Vicarage Road on November 20.