However, after reporting back for pre-season training he made a surprise appearance in the match against Grimsby on Wednesday, playing the whole of the second half.
With first team defenders Andy Dawson and John Anderson injured, manager Peter Taylor could be set to give Strong a second chance at the KC Stadium.
He said: "To be fair to him, Greg Strong has not done anything wrong since I came to the club. It has been a very frustrating time for him but it's not that I don't like him personally or anything like that.
"It's just that I've looked at the other centre halves I've had at the club and he hasn't had a chance.
"If I had to name my team for the start of the season tomorrow then I'd be sure of six or seven places. However, the injuries to Andy and John mean places have suddenly become available.
"I looked at Strong against Grimsby because ideally, I only wanted the players to have a maximum of 45 minutes.
"He did well. For me, if there is a position there to be had then he would be considered."