Benicio Baker-Boaitey has completed a permanent move to the club from FC Porto, after initially joining on loan in January.
The former West Ham winger has signed a contract until June 2023, and will once again link up with the under-23 squad.
Under-23s boss Andrew Crofts said, "Since he came on loan in January, Benicio has shown his ability and worked hard in both training and matches to earn the move.
"We are really looking forward to working with him on his ongoing development this coming season."
Londoner Baker-Boaitey came through the ranks with West Ham, before leaving for Porto at the beginning of the 2020/21 season.