Cuesta will hand the keys to his midfield to the 30-year-old, who has signed a contract running until June 2027 after arriving in the city as a free agent following the collapse of his time in Saudi Arabia.
Sierro terminated his contract with Al-Shabab on 21 August, a year early, and needed barely two weeks to find a new home in a considerably tougher league.
Parma turned to the free-agent market having been left short in midfield by injuries to Tommaso Nicolussi Caviglia and Adrián Bernabé, with club owner Kyle Krause personally signing off on the move — marking the occasion, as is now customary, with a Swiss flag emoji on social media.
Sierro arrives with genuine pedigree: 15 caps for Switzerland, won at the relatively late age of 28 after working his way up through the lower reaches of the game rather than being fast-tracked as a natural-born talent.
National team coach Murat Yakin left him out of his squad for the March friendlies despite his involvement up to that point, explaining simply that "we have a lot of alternatives in midfield — competition in that department is very strong too."
Born in Sion on 8 October 1995, Sierro began his career at his hometown club before a move to Freiburg in Germany at 22 failed to yield regular football. He rebuilt his career back in Switzerland with St Gallen and Young Boys, winning two league titles and a Swiss Cup at the latter, before a fresh attempt at a top-five European league finally arrived at 27 with a move to Toulouse.
There, he took over the captaincy within six months and helped the club win the Coupe de France in his first season, going on to make around 90 appearances and score in double figures before a switch to Saudi Arabia's Al-Shabab last year — a move that may have cost him a place in Switzerland's squad for this year's World Cup, and one he quickly moved to reverse.
Comfortable in possession with a good footballing brain and an eye for a pass, Sierro has also long been Switzerland's preferred penalty-taker and can use both feet effectively, despite being naturally right-footed.
His solid touch and reading of the game aside, he has a habit of chipping in with goals too, having scored 54 times in 413 career appearances — an unusually high return for a player who has spent much of his career playing in deeper midfield roles.