"It's very different," the Spaniard told British media.
"When you are right in the middle of a season, I think players understand that you can't sell someone if you can't replace him.
"We created a squad to see how far we could go over 10 months. January doesn't come into consideration.
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"We'll never lose anyone in January, unless it's somebody who hasn't been playing and we need to find a solution. If he's a top performer, it's not even a consideration.
"January is a window to solve problems with players who are not featuring as often as they feel they should, or to bring in players from a lower league to give them an opportunity."
Martinez added that acquiring English players in the close season would require major investment with their fees driven up by the staggering 5.2 billion pound ($7.82 billion) television rights deal that kicks in prior to the 2016-17 campaign.
"The prices will go up for English players again," the manager said.
"The same players will have more options, so the value of the player will be increased just because of the bargaining.
"The premium of having English players will be more expensive, the premium of having European players will be more expensive and scouting will be important for making better decisions on leagues that people do not usually look to.
"I think the uncertainty comes in the summer, where everyone speaks about possibilities. That's where there's a constant debate and talk."
($1 = 0.6646 pounds)
(Writing by Simon Jennings in Bengaluru; Editing by John O'Brien)
