Sunderland defender George McCartney has joined West Ham on a four-year deal in a move worth £1m.
McCartney made 157 appearances for Sunderland
The Hammers have paid £600,000 for the 25-year-old left-back, who also plays in central defence, with Clive Clarke moving in the opposite direction.
McCartney is out for 10 weeks after injuring a knee in a pre-season game but passed a medical on Monday evening.
He has won 19 Northern Ireland caps but has refused to play while coach Lawrie Sanchez remains in charge of the team.
West Ham would allow Clive, who was our number one target, to come here but only if George went the other way
Sunderland boss Niall Quinn
McCartney is West Ham's sixth signing of the summer as they prepare for a Uefa Cup campaign after just one season back in the Premiership.
Fellow defenders John Pantsil, Tyrone Mears and Jonathan Spector, midfielder Lee Bowyer and striker Carlton Cole have already joined last season's beaten FA Cup finalists.
Sunderland manager Niall Quinn said their need to find a replacement for the injured McCartney was what had brought the deal about.
"We searched for a replacement for George as soon as he got his injury and a deal was struck," he said.
"It cropped up that West Ham would allow us to take Clive, who was our number one target, to come here but only if George went the other way.
"We weighed up the options and it was attractive for us because we've got a player who is ready-made to come into our team now, when we need him."