Tsimikas was forced to miss both of Greece’s UEFA Nations League clashes in the September international break, with the Greek FA confirming two players had returned positive COVID-19 tests.
The left-back subsequently flew back to Merseyside and was not seen in the buildup to the Reds’ Premier League opener against Leeds, with neither Jurgen Klopp nor the club commenting on rumours of his illness.
Klopp’s side visit Stamford Bridge on Sunday, with this week providing the very rare luxury of a full six days of training prior to the clash.
It is unlikely Tsimikas will feature against the Blues, but his return is encouraging ahead of the League Cup third-round tie at Lincoln City next week, which could see the 24-year-old make his competitive debut.
Neco Williams was also involved in training, having missed a session after reporting back from Wales duty, while Harry Wilson and Rhian Brewster were both pictured amid speculation over their futures.
The clash with Lincoln is likely to see Klopp make wholesale changes, with Shaqiri, Koumetio, Elliott, Tsimikas, Williams, Brewster, Adrian, Divock Origi, Curtis Jones, James Milner, Joel Matip and Takumi Minamino all in contention.
Before then, though, is the small matter of a trip to west London, which could see Liverpool make an early statement against a side boosted by heavy spending this summer.
The Premier League confirmed on Monday evening that of 2,131 tested in the latest round of COVID-19 tests, four have returned positive and will enter a 10-day period of self-isolation.