Johnstone has Premier League experience with Wolves, West Brom and Crystal Palace
Celtic have completed loan deals for former England goalkeeper Sam Johnstone and teenage Chelsea duo Shumaira Mheuka and Landon Emenalo.
Johnstone, 33, arrives from Wolverhampton Wanderers and will provide competition for Finland international Viljami Sinisalo.
Striker Mheuka, 18, has extended his contract at Chelsea until 2031, having made nine outings for the London club.
Four of those came in the 2024-25 Conference League, including his only start. Last season, he captained the Chelsea Under-21 side, scoring 18 goals in 19 games.
Emenalo, 18, also joins on loan from the London club and will offer cover for Kieran Tierney at left-back.
He made 14 Premier League two appearances for Chelsea's Under-21 team last season and set up three goals in those outings.
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Johnstone, who won the last of his four England caps in 2023, made 17 appearances last season but lost his starting place at relegated Wolves in December and has not played since an FA Cup loss to Liverpool in early March.
"I'm buzzing to be here and I'm excited to get going," said the goalkeeper, who began his career at Manchester United and has had spells at Aston Villa, West Bromwich Albion and Crystal Palce.
"I didn't need convincing by anyone, but Joe Hart rang me the other day just to reiterate what a place this is, what a great group of lads and how the fans are unbelievable.
"You hear about the size of the club, but just being here for a day, you notice how big the club is. And the pressure to win, which is what I like – pressure to win, pressure to perform and we all want to win trophies."
Kasper Schmeichel had been first choice at Celtic since the summer of 2024, but played his last game in February and subsequently retired due to a shoulder injury.
