The Gambia winger arrived this week from Newcastle United.
“We've been tracking Yankuba for a while," Weir told the club's website. "He spent last year on loan at Feyenoord and we watched him closely in that loan move.
“Then when the opportunity came up for us to bring him here we were really excited at that prospect.
“He's only 19 and he's not played in the Premier League before, but he's played at a really good level. It’s an area that is important to us - attacking players with pace, with a pedigree who are playing at a really good level.
“We've got to give him time and be patient which I think we've shown that we will do with a number of players. He is someone we're looking forward to working with.”
Weir added, “Identifying players and finding them is relatively easy. The hard part is bringing them to your club.
“What we have shown is that we are a club that gives young players opportunities. We bring in great head coaches. We make players better. That message is really strong and powerful.
“Maybe we cannot compete with the salaries some others can offer but we can compete on pathway, opportunity and development. For the right players and agents that is really important and really powerful. Our reputation in the game now is such that we are that type of club.
“That is what we have to compete with and utilise to attract the best players no matter what age they are.”