The 16-year-old youngster, who has been on trial with Blues from the Premier League outfit since earlier in the season, has already impressed the coaching staff with his performances.
The attacking midfielder, who was with the Cottagers from the age of 12, has found the back of the net four times in six appearances for Blues U18s.
He has previously been involved in the England U16 set-up, but has yet to make an appearance for the Young Lions.
Academy coach Steve Spooner says Blues are delighted to be able to bring McDonald in. “Wes is quick, powerful and scores goals," he said.
"He’s only small but is a really powerful boy who has an eye for goal. He likes to take people on as well.
"He wanted to leave Fulham and they agreed to let him go if all the details could be met, which they were. The boy was very happy to come and join us."