The 27-year-old has already had a tough stretch with injuries, fingers crossed he recovers as quickly as possible and without complication.
The news will resonate strongly with Ireland and Everton fans, following Seamus Coleman's leg break against Wales a year ago.
Only the intervention of McCarthy prevented Rondon from the opportunity of doubling their lead just after the hour.
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"All our thoughts are with James McCarthy this evening after it was confirmed he has suffered a double leg fracture", another tweet said. I think it very much depends on the specialist or surgeon that deals with it. "It's a big blow for him and us".
West Brom went ahead when Jay Rodriguez slotted the ball past goalkeeper Jordan Pickford in the seventh minute after Polish midfielder Grzegorz Krychowiak struck a sublime pass in behind the defence with the outside of his right foot.
"Now this is one serious injury which we know will keep him out until next season at some stage, that's a big blow".
Rondon appeared distraught after the collision and was consoled on the pitch by West Brom manager Alan Pardew. "He heard the break. that affected him because he is that kind of person".