According to The Athletic’s Simon Johnson and David Ornstein, Lampard was furious after he had found out that Alonso headed straight to the team bus, after he was substituted at half-time.
The Athletic report states that even though both Alonso and Mateo Kovacic were taken off at half-time, only the Croatian re-emerged to watch the second half from the stands.
The Athletic are also reporting that Chelsea staff themselves were surprised to see Alonso away from the designated area for the away team at The Hawthorns. In a time when the Premier League have strict operating procedures due to COVID-19, Alonso's actions came as a shock to Chelsea staff, before Lampard vented his fury straight at Alonso.
The Athletic have quoted Chelsea insiders as saying that Lampard was "the angriest they’ve ever seen him" during his tirade towards Alonso in the dressing room after the game.
Fallout could lead to Marcos Alonso move from Chelsea
The fallout of this incident could see Alonso leave Chelsea this summer. He was anyway not going to be the no.1 left-back for too long, with the Blues having signed Ben Chilwell from Leicester City in the summer.
With a week left for the transfer window to shut, Alonso could now be on his way out, especially after a public dressing down from the manager.
Even after the game had finished, Lampard blamed Alonso's "clear mistakes", as Chelsea only managed a point in a 3-3 draw against West Bromwich Albion.
“The first one Marcos heads it into the middle of the pitch for them for a transition,” Lampard said.
“Marcos loses his man for the third goal from the corner, a clear mistake. You can do as many meetings as you want, if you are going to make those mistakes you give yourself a mountain to climb.”
The Athletic have also reported that some Chelsea insiders have said that they would be surprised if Alonso ever plays for Chelsea again.
With Chilwell also close to full fitness again, Alonso is unlikely to play a big role for Chelsea for the rest of the season anyway. However, with limited time left in the transfer window, it remains to be seen if he will indeed leave the club.