RB Leipzig's Emil Forsberg in hope of playing Champions League football next year, as Leipzig wait ruling to play in next year's competition.
Vallejo, 20, is in the final weeks of his loan at the Bundesliga club, for whom he has made 25 appearances.
Wood, who missed Sunday's 2-1 defeat at Werder Bremen with a knee injury, could play a role against bottom of the table Darmstadt.
Ousmane Dembele to Manchester United and Romelu Lukaku to Chelsea are two of Wednesday's emerging whispers.
Hamburg have opened talks with U.S. international Bobby Wood about a long-term contract extension, sporting director Jens Todt has told Sport Bild.
The Mexico international, who has 10 goals this season, resumed training on Tuesday.