The defender was forced out of the Blues' Champions League draw with Dynamo Kiev, but revealed he only suffered a dead leg and the club are confident he will be fit for Sunday
Vincent Kompany had already departed the scene with a recurrence of his calf issues by the time Otamendi was forced off at the Etihad Stadium, where City went on to draw 0-0 and seal progression to the quarter-finals.
The Argentina centre-back attempted to stay on but finally admitted defeat after playing two long balls, which only seemed to exacerbate the issue.
But he insists the problem is not serious and, furthermore, Goal understands City are confident he will be fully fit within two to three days, clearing him for Sunday's clash.
"It was something similar to a dead leg," he told reporters. "I will have tests [on Wednesday], but as the knock was so strong, it stopped me from continuing and I preferred to go off.
"I’ll go for tests, but obviously I hope it’s not anything. We hope everything will go well and hope I can be there against United."
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City laboured for much of the clash against the Ukrainian side, only mustering a goalless draw, but made it through to the last eight for the first time in the club's history courtesy of a 3-1 first-leg win.
And despite watching from the sidelines, Otamendi went home in a positive mood.
"I am happy because we have achieved our objective, which was to qualify for the next round, so really happy have to have progressed, really happy."