Goalkeeper Petr Cech has been named in Chelsea's Premier League squad - despite having retired from playing at the end of the 2018-19 season.
The 38-year-old, who is the club's technical and performance adviser, was added as "emergency cover".
Elsewhere, midfielder Mesut Ozil has been left out of Arsenal's 25-man post-transfer window squad.
Manchester United have not included defender Phil Jones and goalkeeper Sergio Romero in their list.
English centre-back Jones, 28, last played for United in an FA Cup win over Tranmere Rovers in January, while 33-year-old Argentine Romero - who was linked with a move to Everton on transfer deadline day - has moved down the pecking order following the return of England international Dean Henderson from Sheffield United.
Clubs had to name a 25-man squad after the closure of both the international and domestic transfer windows.
'It is a no-brainer to have Cech in the squad'
Cech spent 11 years as a player at Stamford Bridge, winning 13 trophies, including four Premier League titles and the Champions League.
He last played for the Blues in the 3-1 win over Sunderland in May 2015, before joining London rivals Arsenal.
The former Czech Republic international then returned to Chelsea in the summer of 2019 to take up his new role and has recently been helping with the goalkeeping coaching.
"It's definitely not done for the romance. Pete enjoys the training, that's how he is," said Blues manager Frank Lampard.
"With Pete, it's something I wouldn't expect to happen, but with how fit he is if we were in crisis we couldn't have anyone better than Petr Cech around.
"I don't expect him to play, but nobody expected what's happened in the last six or seven months, so that would explain why he's in there.
"We had a space this year, and Covid makes this a year like no other. He's very fit, he's still relatively young, and he finished playing when he possibly could have carried on.
"It's a total no-brainer to have him in the squad."
Cech is one of four goalkeepers in Chelsea's squad. Spaniard Kepa Arrizabalaga, the world's most expensive keeper, has endured indifferent form since the restart of the previous season, while new signing Edouard Mendy made his return from injury against Sevilla on Tuesday.
Willy Caballero, 39, has twice played for the Blues this season and is usually selected in the domestic cup competitions.
Ozil, 32, who joined Arsenal for a then club record £42.4m in 2013, has not played for the Gunners since 7 March.
The German, who had also been left out of their Europa League squad, will now only be able to play for Arsenal Under-23s until his deal expires in summer 2021.
Greece defender Sokratis Papastathopoulos was also omitted.