As reported by Portuguese newspaper A Bola, Martinez's agent told Portuguese radio station Antena 1 that his player could be presented with a number of opportunities to move before the World Cup.
Martinez was the top scorer in the Portuguese top flight, which prompted speculation he could move to a Premier League club like Chelsea or United, while Porto finished a disappointing third behind Sporting and league winners Benfica this term.
Speaking to Antena 1, Luís Henrique Pompeu said: "There are clubs interested in knowing more about his situation and they may make offers to FC Porto, if convenient to all parties. It will be a normal process done calmly and transparently."
The £40m-rated Martinez leads Liga Sagres with 20 goals in 30 games this season, and the Colombian international is expected to lead the line for his country with Radamel Falcao recovering from long-term injury.
Both Chelsea and United scouted Martinez towards the end of this season, although neither Premier League team reportedly has the Porto star at the top of their shortlist.
Chelsea are looking for another striker, with boss Jose Mourinho very public in his frustration at the output of his current group of forwards. United meanwhile, may look to wait until a new manager is brought in before adding to their squad.