Steve Bruce let Danny Collins join Stoke because he felt he was close to landing a replacement.
The Sunderland boss also insists the £3.3million offer lodged by the Potters was 'too good to turn down'.
The sale of the popular centre-half came as something of a surprise, with Collins having been named the Black Cats' Player of the Year by supporters for the past two seasons.
His versatility was also considered to be vital to the club's cause, with the Wales international providing cover at left-back.
It transpires that his services would have been required in that area at Sunderland had he remained at the Stadium of Light, with Georgre McCartney currently sidelined.
Bruce, though, insists he was close to landing cover in that department on transfer deadline day - believed to be Wigan's Maynor Figueroa - and claims that persuaded him to let Collins leave.
"I can understand why people were surprised about Danny moving on, because he was a popular player here and the fans liked him for his willingness to put his foot in for the cause," Bruce said in the Sunderland Echo.
"I also know he offers genuine cover at left-back, which is an area highlighted because of the injury to George.
"But, as it happens, I thought we were getting a left-back in on deadline day - the deal was practically done, but, at the very last minute, it didn't come off.
"Then I had to consider the fact Stoke were still interested in Danny.
"I had allowed him to speak to them, he was down there in talks and I thought the offer was too good to turn down for a player approaching 30.
"It means that I'm short of cover at left-back until the next transfer window opens, but we have George and, if he's not available, we do have other options.
"It's a fact of life that with the planned left-back not arriving, it makes things a little awkward for us.
"It's not ideal. But long-term I think the deal for Danny was a good one at the time and I know I'll be judged on it depending on how things eventually work out."