"He has been advised rest and it appears that he may be able to play soon. We expect Postiga to continue playing a vital part in the team's goal to lift the trophy for the second time," the Kolkata franchise said without making clear whether Postiga would be fit for the next match.
The Portuguese World Cupper, who was ruled out because of an injury after a 72-minute appearance last season, has suffered a rib injury in their 1-0 win over Kerala Blasters in Kochi.
"The test reports which came sometime back shows there is no reason of worry and the injury is a minor one."
ATK have one draw and one win, while Mumbai are in rampaging form with two wins from as many matches.
Mumbai have roped in Uruguayan super start Diego Forlan who was reportedly in talks with ATK but the deal failed to materialise as the Kolkata franchise retained Postiga for another season.
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