With Reading in mid-table in the Championship, out of play-off contention and clear of relegation danger, the pair have returned to their parent club to be assessed and to train with the Blues for the remainder of the season.
English defender Hector, 23, and Brazilian midfielder Piazon, 22, will not be eligible for selection in the Blues’ remaining four Premier League fixtures under caretaker boss Guus Hiddink, a story on the club website stated.
Hiddink will make way at the end of the season, with Antonio Conte joining as head coach once Italy’s European Championships campaign is complete.
Their assessment is likely to determine if they should stay with the first team next season, or be made available for a further loan.
Hector signed from Reading on a permanent deal at the end of the 2015 summer transfer window, but was immediately loaned back to the Championship side. He has made 35 appearances for the Royals this season.
Piazon, who joined Chelsea in August 2011 and has a handful of first-team appearances, has scored five times in 27 appearances for Reading this season.