Chelsea's strikers will love playing with Juan Cuadrado if he does join, says Thierry Henry.
Manchester United boss Louis van Gaal has said that Darren Fletcher's proposed move to West Ham is off.
Saints revealed the Perth-born former Scotland Under-21 international had signed a two-year contract following the expiry of his Easter Road deal.
The 23-year-old, who can also play right-back, made more than 150 appearances for Hibs, including 38 last season, but missed out on a place in the William Hill Scottish Cup final squad for the second year running.
Wotherspoon is manager Tommy Wright's second signing after he renewed 20-year-old Gwion Edwards' loan deal from Swansea until the end of the year.
The midfield pair's arrival comes days after St Johnstone agreed a deal with Ross County to allow Richie Brittain to renege on the pre-contract he signed with the Europa League qualifiers in January.