Local media reported that fullback Fabio Coentrao had returned late from the Christmas and New Year break and coach Jose Mourinho had demanded the stiffest possible punishment for his Portuguese compatriot.
A club spokesman declined to confirm the reports but they are the latest distraction for a team that needs to focus all its energy on getting back to winning ways and cutting the yawning 16-point gap to unbeaten leaders Barcelona.
Coentrao's indiscipline adds to Mourinho's selection problems in defence, with Pepe recovering from ankle surgery, fellow centre-back Sergio Ramos suspended and full-back Marcelo out injured.
"The important thing is to win and be together, both the team and the fans," Ronaldo told a news conference.
"The league is tough, but it is still mathematically possible for us to win and we have to keep the belief until the end," the Portuguese international added. "It will be an uphill struggle."
Promising winger Isaac Cuenca, brought into the first team under Vilanova's predecessor Pep Guardiola, also trained with his team-mates as he continues his recuperation from a serious knee injury sustained at the end of last season.
"The absences of Falcao, Arda and Miranda will give other players a chance, which is good for the team," Simeone told a news conference on Wednesday.
"Arda is definitely not leaving," he said. "He has a contract with the club and he is an extremely important player and he will prove that where he has to prove it."
