The Cameroon defender has barely missed a match in the last four seasons but he sat out Sunday's 3-1 win over Reading after a niggling injury flared up. Villas-Boas said after the game that the 28-year-old may have to undergo a minor operation to rectify the problem.
"Benoit has a small fragment in his knee that makes it swell a lot," Villas-Boas said. "He has played through pain in the last couple of games. His knee may have to be washed up and if that happens we are looking at a four-week absence."
Kyle Naughton usually operates at right-back but he slotted in to Assou-Ekotto's position comfortably against the Royals and Villas-Boas also has the option of shifting Jan Vertonghen to left-back, where he has played numerous times for Belgium.