The Portuguese marksman has been drafted in on a six month loan deal as cover for Wilfried Bony, who goes to the African Cup of Nations with the Ivory Coast in January.
“I’m very happy to have signed him,” said Monk.
“He’s a very good player. His name came up in the summer, but for whatever reasons that did not happen, but we are delighted to have him here now.
“I’ve already said we needed someone with Wilfried going away and Nelson gives us another option.”
Monk wasn’t just looking for any striker to cover Bony, he believes that Oliveira poses a different threat to Gomis and the Ivorian, adding another string to the bow of the Swansea City attack.
“We were talking about diversity and different types of strikers and that is what Nelson gives us,” explained the for centre half.
“He’s different from Wilfried and Bafi too, just as Bafi is different to Wilfried. He gives us options.
“We know all about what Nelson can do. It will be a good challenge for him too. He’s a lovely guy and will just want to start training now and start working hard.
“He can’t play until January, but we wanted him earlier so he can train with us.”
As one striker comes into the club, Monk could face losing another after Bafetimbi Gomis was linked with a number of clubs, including Crystal Palace.
“I can’t control players been linked with other clubs, but Bafi is a Swansea City player,” insisted Monk.
“With Wilfried going he is going to be needed, He is a top, top player.
“It has been difficult to give him game time with Wilfried playing so well, but Bafi has been great about it.
“He has not said anything and just wants to get on with things. He’s going to play a big part for us now.”
Next up the Swans welcome Aston Villa to the Liberty Stadium on Boxing Day.