SPORTING Lisbon have already had a couple of offers turned down, with FC Porto and PSV Eindhoven just two of a number of other clubs known to be showing an interest.
Sadly for Aberdeen, however, the wheels of the transfer market are unlikely to move quickly enough for Filip Kostic to be spirited away from FC Groningen ahead of Thursday's Europa League second qualifying round tie at Pittodrie.
The 21-year-old Serb enjoyed a fine season last term, producing nine league goals and seven assists as Erwin van de Looi's side ended a seven-year absence from Uefa competition by emerging from the play-off system that takes in the four teams who finish from fifth to eighth in the Eredivisie.
One of their main strengths during a 10-game unbeaten run at the end of the campaign was their ability to hit on the counter. Kostic, a fast and technically-gifted left winger, was an integral element of that game plan and is in line to feature heavily as Groningen endeavour to put themselves in a strong position during this week's first- leg fixture in the Granite City.
Kostic was brought in from Radnicki Nis two years ago for around €1 million, but failed to make any impression in his debut season. However, van de Looi , after taking over from the one-time Motherwell defender Robert Maaskant as head coach, saw a rough diamond that could be quickly buffed into shape and has made fantastic progress with him over the course of 12 months.
Theo Snelders, the former Aberdeen goalkeeper now on the coaching staff of FC Twente Enschede, has warned his old club they must not allow themselves to become too stretched and open to being hit on the break as they look to establish the advantage at home because Kostic is exactly the kind of player capable of punishing them.
"Groningen are a good team on the counter-attack as they proved when beating Vitesse 4-1 away from home in the semi-finals of the play-offs," said Snelders. "The counter-attack is a real weapon for them and Kostic is important in that.
"He really is something special. After a slow start, he played regularly last season and is very skilful and a good dribbler. He likes to take players on."
Groningen have already sold their teenage striker Richairo Zivkovic to Ajax for €2.5m and had agreed a deal with the Saudi Arabian club, Al Ahli, to cash in on the attacking midfielder, Tjaronn Chery.That deal, however, collapsed over financial issues and has yet to be resurrected. Snelders believes that is bad news for Aberdeen as Chery has taken on the role of being their playmaker and brings some very particular dangers.
"Set-pieces are going to be a major part of Groningen's armoury as well," he said. "Chery plays in the No 10 position. He is small, but he is very strong and dangerous at the free-kicks.
"Groningen did sell a very big talent in Zivkovic to Ajax over the summer and their goalkeeper, Marco Bizot, to Racing Genk, but Sergio Padt has come from KAA Gent to replace him.
"I think it will be very close over the two legs. Aberdeen, from what I have seen, have improved and playing those two competitive games against Daugava Riga and scoring so many goals may help.
"Groningen have only been playing friendly matches against much lower-level opposition."
Snelders spent eight years at Aberdeen as a player between 1988 and 1996 and won both the Scottish Cup and League Cup during a successful spell there.
He returned to his old stomping ground with FC Twente 12 months ago for a friendly match, which the home side won 2-0, and took the opportunity to quiz Derek McInnes, a former team-mate from Rangers, on his plans to have the club challenging again for silverware.
McInnes was as good as his word. The League Cup finds itself safely housed in the trophy room in the wake of his debut season at the helm and Snelders admits that being there at the beginning of his mini-revolution was enough to convince him that better times were looming.
"I spoke to Derek before the game last summer and was really impressed with him," recalled Snelders. "He spoke in much wider terms than just looking to improve results. He wanted to change things at the club, give it a good, strong foundation.
"Aberdeen were underachieving and I think it was maybe a good time for him to step in there. Derek was an intelligent player with tactical awareness and these are the guys who usually make that move into coaching, so it doesn't surprise me he has done well.
"I saw the highlights of the League Cup win last season. The crowd that went to Celtic Park for that game tells you the potential that exists at Aberdeen."