If it feels there is an issue, the OFT can recommend a full Competition Commission inquiry. The Commission, in turn, could potentially block the deal.
Last year Amstrad supplied around 30% of the set-top boxes purchased by Sky.
The Amstrad deal netted founder Sir Alan Sugar a windfall of nearly £35m. Sky said the deal will boost the company's design and development arm.
Sky is currently the subject of a compeition probe over its stake in ITV.