It comes after another squad overhaul took place with eight players departing, while five new faces arrived at Fratton Park.
But despite the acquisition of players from the Premier League and Championship, the club have come under criticism in recent weeks after failing to sign a new midfielder.
Danny Cowley has limited options in the department following Shaun Williams’ long-term injury sustained against Charlton – proceeding Joe Morrell’s potential ban after receiving a red card against Oxford United on Saturday.
But Cullen has called for patience while new signings settle, before explaining how work for summer recruits has already begun.
He said in his pre-Burton programme notes: ‘Last Thursday I gave an interview to the club’s YouTube channel, reflecting on the window, which saw a total of 13 player transactions, and to set out the strategy worked out ahead of Christmas with Danny.
‘I tried to set out an honest appraisal and I hope the background was helpful to supporters. Ultimately, the success of any summer or January window will be judged by the end of the season, but what is also important is that last month’s business aligns to the direction of what we are seeking to do in terms of long-term recruitment.
‘The signing and fee paid for Denver – a player under 24, on the way up and with first team experience – is indicative of the club’s strategy and will be a big part of our strategic focus for the summer.
‘Which has already started.’
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