West Ham manager Sam Allardyce chose to sign striker Andy Carroll over Swansea top scorer Wilfried Bony last summer.
Bony, set to start at Upton Park on Sunday, signed from Vitesse Arnhem for £12m and has scored six league goals this season after 16 last time round.
Allardcye said: "It was a case of one or the other. We couldn't do both with the budget we had."
West Ham's wins over Newcastle and West Brom this week leave them in fifth place in the Premier League with Allardyce, who admitted making an initial bid for Bony, delivering on his promise to bring a new brand of attacking football to the Londoners.
|Andy Carroll's injury record at West Ham|
|September 2012: Picks up hamstring injury in his first game on loan - out for a month|
|November 2012: Twists knee against Manchester United - sidelined for two months|
|May 2013: Damages heel in the last game of the season - out for seven months|
|July 2014: Tears ankle ligaments in pre-season - out for four months|
Swansea though are just two places and two points below the Hammers and Allardyce knows, in Ivory Coast's Bony, the Welshmen have a striker capable of causing defences damage.
"It'll be very difficult to contain him because he's in such good form," he said. "We'll have to limit the supply into him from the midfield and wide men.
"We need to get tight to him but not too tight because he can roll defenders well, he's strong and very skilful.
"To try and knock him off the ball is not an easy task. It'll be a good test for our lads to play against a player who's in such good form."
Carroll, 25, has started just two matches for West Ham this season after returning from four months out following ankle surgery. He missed the majority of 2013-14 with a heel problem.
He cost Liverpool £35m in January 2011 but was loaned to West Ham in August, scoring seven goals in 24 games.