Gareth Bale is facing a race to be fit for Tottenham's Champions League quarter-final first-leg tie against Real Madrid in Spain on 5 April.
Spurs say he suffered a hamstring strain while on international duty with Wales, who insist he already had the injury before joining the squad.
The 21-year-old withdrew from Gary Speed's squad to face England last Saturday after pulling up in training.
A subsequent scan revealed he was suffering from a grade one strain.
The recovery time for such an injury is usually between seven and 10 days.
"Gareth has returned to Spurs Lodge and took part in controlled straight-line running so we could assess him," said a statement on the Spurs website.
"We sent him for an ultrasound scan examination and that has confirmed the presence of a minor grade one hamstring strain.
"Gareth has reported no pain or stiffness after taking part in the running and we shall continue to monitor him and see how he responds to his conditioning programme throughout the week."
Tottenham became embroiled in a club-versus-country row after the Football Association of Wales (FAW) claimed that Bale had suffered the injury before reporting for international duty.
"The scan revealed that Gareth Bale picked up his injury last week," said a statement on the FAW website.
Spurs boss Harry Redknapp hit back at those suggestions, saying that the former Southampton winger was fully fit when he left Tottenham to join up with Wales after the club's recent 0-0 draw against West Ham.
Tottenham's head of medical services Wayne Diesel echoed Redknapp's claims, saying: "Gareth did not report any hamstring issues when we assessed our players after our fixture with West Ham United which means he was free to report for international duty.
"Nor did the Football Association of Wales raise any problems with us prior to his first training session with the national team on Tuesday following two days of rest.
"He was passed fit to train by the FAW medical team and it was only after 40 minutes of his first training session on Tuesday, which included some high intensity runs, Gareth complained of tightness in his right hamstring and was pulled out of the remainder of the session as a precaution.
"We requested the player be sent immediately for a scan which subsequently revealed the hamstring strain that forced his withdrawal from the squad."
Bale has missed a large part of the last three months with a back injury that he sustained against Newcastle in January.
The problem kept him out of the first leg of the club's last-16 win over AC Milan and restricted him to a substitute appearance in the return leg.
The goalless draw with the Hammers was his first start for the club in two months.