After predominantly being used as a bench player this season, the 25-year-old has become a key player for Porto in recent weeks.
The Serbia international scored the winning goal in Porto's 3-2 win over Famalicao.
The Reds want at least €20m, but that is out of Porto's price-range.
However, the Portuguese giants are waiting until the end of the season to speak with Liverpool about a potential deal.
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