The England man is available for £15 million from United.
Also revealing talks with free agent Samuel Eto'o, Martinez said: "There’s a lot of money involved in those two [Welbeck and Eto’o].
“At the moment, if I’m honest with you, I’m looking at all the options.
“While the window is open, we are looking at anyone who can help us and also looking at our injured players and seeing how they react. Oviedo and Kone will have a big say on how we end the window.”
For the big stories and the banter follow us on Twitter: @tribalfootball