Sunderland had a bid of €35 million plus €5 million in add-ons rejected by Sporting over the summer after the Portuguese club demanded a guaranteed €40 million for the winger, but the Black Cats have continued to track his performances closely ever since, refusing to give up on a deal despite the setback.
According to Record, a representative from the Stadium of Light was present at Sporting's 3-1 Champions League win over Galatasaray, with a specific focus on Catamo, who scored a spectacular goal to spark his side's comeback in that match.
The Mozambique international's form since the summer has only strengthened Sunderland's resolve, with the club believed to be ready to revisit their interest as soon as the January window opens.
Whether the improved performances are enough to convince Sporting to accept a fee closer to Sunderland's previous offer, rather than their original demand, remains to be seen, though the north east club may yet need to find the extra five million euros that separated the two sides in the summer.
Como, managed by Cesc Fabregas, made preliminary enquiries about Catamo during the same window without progressing talks, while Tottenham and unspecified clubs in Saudi Arabia have also been credited with an interest in the winger, adding to the sense that competition for his signature could intensify significantly if he continues in this vein of form.
Catamo has become an increasingly important figure for Sporting since establishing himself in their first team, and his continued excellent form is likely to keep his valuation high, or push it even higher, the longer any transfer decision is delayed. He has represented Mozambique at senior international level and is regarded as one of the standout performers in Sporting's squad this season, operating primarily as a wide forward capable of playing off either flank.