The 18 year-old will leave Djurgarden for Spurs this summer.
Discussing Bergvall and FC Copenhagen's Roony Bardghji, Tomasson said: "They are fantastic players and they can get into my squad. I work closely with Daniel Bckstrm on this. We will analyze their matches and ultimately they have to perform.
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"But if you look at my history as a coach, I have previously used young players to a large extent. They will get the chance if they are good enough.
"Players who have been part of the squad for a long time should also get a chance now. But they also have to perform. Ultimately, it all comes down to how the players perform. That is my message to the players."