Jose Mourinho says the form of Giovani Lo Celso is giving Tottenham "an easy decision" to sign him on a permanent basis.
A superb individual run from Lo Celso helped to set up Spurs' goal as Son Heung-min struck in the 1-1 FA Cup fourth-round draw against Southampton on Saturday.
The 23-year-old also had a goal disallowed and Mourinho is sure he has done enough to earn a permanent place at Spurs, having initially joined on a season-long loan from Real Betis, with an option to buy.
Mourinho said: "It's not an obligation, it's an option. I think the boy is earning the decision.
"He's making an easy decision for the club to execute the option. Incredible evolution since I arrived.
"Barely played a game [before I arrived], I think he played against Red Star Belgrade and with me it was a little bit difficult to come in the first few weeks.
"But he understood what we wanted. Good learner, good kid and I think by himself he made the decision that the club is going to execute the option. That's normal, he earned it."
Son, meanwhile, has netted in back-to-back matches at a time where star striker Harry Kane is out injured.
Mourinho, whose side will now play an FA Cup replay against Saints, added of Son: "All of the attacking players need this happiness of scoring goals.
"In the first half he had one easier than the goal he scored, facing the keeper the angle was good, the shot was good but for inches he missed.
"It is a good goal, an important goal, so it is good for him.
"Playing a replay will affect [our mid-season break] a little bit. There is one more match we have to play. It is not a personal situation, Ralph Hasenhuttl was telling me the same, we don't need one more match.
"But I think both me and him prefer to play again than to be out. No drama, let's go."