However, Article 3 of the UEFA Cup regulations state: "On entering the competition participating clubs agree: d) to field their strongest team throughout the competition."
Both Villa and Spurs went out of the UEFA Cup on Thursday night after their managers made wholesale changes for the matches against CSKA Moscow and Shakhtar Donetsk.
UEFA however believe it would be too difficult to prove that the rules had been broken in a way which could lead to disciplinary action.
UEFA spokesman Rob Faulkner said: "Clubs are expected to uphold the spirit of fair play and respect their opponents as well.
"The competition regulations do state clubs should field their strongest team."