The Express & Star understands the 31-year-old midfielder is on the verge of joining from Monaco.
Moutinho has been 113 times by Portugal and his signing could be announced as early as today (Monday).
He has been with Monaco for five years and was previously with Portuguese clubs Porto and Sporting.
Moutinho's agent Jorge Mendes has brokered the deal, which comes despite him signing a new two and a half year contract with Monaco in March.
If he deal is completed he will join fellow Portugal internationals Ruben Neves, Rui Patricio and Ivan Cavaleiro at the club as well as Diogo Jota and Ruben Vinagre who have represented their country at youth level.
The 5ft 7in central midfielder played three times at the recent World Cup, starting against Spain and Morocco and coming off the bench against Iran.