Reading pair Sean Morrison and Jordan Obita have both signed new contracts at the Madejski Stadium.
Ipswich defender Aaron Cresswell has signed a two-year extension to his contract.
Tom Cleverley spent the 2010-11 season with the Latics and the club are now set to agree a loan deal for Henriquez, an 18-year-old Chilean forward.
Martinez cannot wait to link up with the talented youngster and is expecting goals.
"Angelo is as good a goalscorer as you will find," said Martinez, quoted in the Daily Mirror.
"He scored goals at Universidad de Chile and he is going to score goals here.
"I am sure he will be an important player for United.
"We are glad we can work with him and he can use Wigan as Tom Cleverley did and adapt to what is needed in this league."
Henriquez joined United in September and made his international debut for Chile last month, marking the occasion with a late goal against Serbia.