Blackburn boss Mark Hughes has admitted it was important he kept hold of Ryan Nelsen.
Portsmouth tried to sign the New Zealand international at the start of the season, but Blackburn rejected their overtures.
Nelsen has only recently returned to action after a lengthy absence and Hughes believes the central defender is among the best buys ever after signing him for free from DC United 18 months ago.
"Having just lost Craig Bellamy to Liverpool last summer, it would have been careless to lose Ryan as well," said Hughes.
"It was strong interest from Portsmouth and big numbers were being talked about but it was important that the club were strong enough to turn it down.
"I recently heard Glenn Roeder saying that taking Antoine Sibierski to Newcastle on a free transfer was the best free signing of the season.
"But Ryan has to be the best free transfer ever - considering the impact he has made since arriving.
"He had never played at this level before but adapted quickly and is a fantastic addition to the squad."