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David Price, Johnny Cueto, Zack Greinke and Jordan Zimmermann are widely regarded as the top four pitchers on the free-agent market.
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Price and Cueto might be most attractive because Draft compensation would not be required to get them. They were both traded midseason, and therefore, couldn't be extended qualifying offers.
"These are only guesses at this time -- but going into the wintertime and with conversations we've had with clubs over the last month, my thought process is most likely any acquisition we'd make in the starting pitching would first happen as far as the free-agent field is concerned," said Dombrowski. "You never know, but that would be my guess. I thought that our acquisition of the relief pitching aspect would more likely come through a trade.
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"We're in a spot that this is probably our major acquisition for the wintertime as far as the trade market is concerned. You never can tell, but that's what my instincts tell me."
The Red Sox have lacked an ace ever since July 31, 2014 -- the day Jon Lester and John Lackey were both traded.
Dombrowski has stated all along that it is almost essential for a team with championship aspirations to have a true No. 1 starter.
Ian Browne is a reporter for MLB.com. Read his blog, Brownie Points, and follow him on Twitter @IanMBrowne. This story was not subject to the approval of Major League Baseball or its clubs.