David Moyes was spotted at Atletico Madrid's Stadium during their Champions League game against Porto, and many Spanish reports suggest that the Manchester United manager was scouting Koke.
The United boss has recently admitted that United could spend big money in January, and the Atletico playmaker has been earmarked as one of their main objectives to arrest their slump in the Premier League - where they have lost five of their first 15 Premier League games and are ninth in the table.
Koke, who is reportedly available in January for a fee of £15m, started Atletico's match against Porto and played a key role as the Madrid club, who had already sealed top spot, emerged comfortable 2-0 winners.
After the game the 21-year-old was asked about Moyes' visit, but played down reports of a move to Old Trafford.
"I didn't know he was here. I'm not worried, I renewed my contract this summer" he told reporters.
Koke, a product of Atletico's youth system, extended his contract until 2018 earlier this year, and received a significant pay rise.
The midfielder is proving to be a sensation in La Liga this season, with eight assists and scored three goals in 15 league appearances. He is reportedly keen to stay in Spain, despite the interest from United and Liverpool.
Atletico sporting director Jose Luis Caminero admitted that he spoke to United manager, but was unable to give an update on Moyes' visit to the Vicente Calderon.
"We spoke, but he didn't tell me exactly why he had come ... I suppose he came to see us because Atletico are a Champions League team and because they also qualified for the last 16," Caminero told Canal Plus.
After the failures of last summer's transfer window, with Cesc Fabregas and Ander Herrera rejecting a move to Old Trafford, United are desperate to secure the services of a high-profile midfielder in January.
However reports suggests they will face competition from several clubs, including AC Milan and Real Madrid as well as Liverpool, should Koke decide to leave Atletico.