Former West Ham captain Kevin Nolan has returned to the club as part of David Moyes' coaching team.
Nolan, who made over 150 appearances for the Hammers between 2011 and 2015, has been out of management since leaving Notts County in August 2018.
As well as Nolan, former Brighton and Norwich coach Paul Nevin will also join Moyes' staff, with both given contracts until the end of the season.
Live Renault Super Sunday
Moyes replaced Manuel Pellegrini as West Ham manager in December, but had only been able to add Alan Irvine as his assistant coach.
"We welcome Kevin and Paul to the club and look forward to working with them," Moyes told West Ham's official website. "Both have a wealth of experience in the game and I'm sure they will make a very positive contribution between now and the end of the season.
"Kevin obviously knows the club very well having played here previously, while Paul's coaching pedigree is excellent. It has taken some time to finalise the coaching staff, but I wanted to make sure I brought in the right people to help us, and both Kevin and Paul are fantastic additions.
"They will get working right away and we are all completely focused on the job we need to do in the coming weeks and months."
West Ham currently sit 18th in the Premier League and face a daunting run of fixtures, with away matches against Manchester City and Liverpool either side of the winter break.
January signing Jarrod Bowen could make his debut in the match at the Etihad Stadium on Sunday, live on Sky Sports Main Event.