The Barcelona midfielder was injured during Spain's 1-1 draw with Switzerland last week and was unable to take part in training on Sunday.
After undergoing an MRI scan on Monday, the extent of the damage was revealed by Spain on their official Twitter account.
⚠️ OFICIAL | Tras las últimas pruebas realizadas a nuestro jugador Sergio Busquets (@5sergiob):— Selección Española de Fútbol (@SeFutbol) November 16, 2020
➡️ Se confirma el esguince leve en el ligamento lateral externo de su rodilla izquierda.
➡️ El centrocampista del @FCBarcelona causa baja para el encuentro ante Alemania. pic.twitter.com/vrqN9cvQNM
Busquets is definitely out of the home match against Germany, which La Roja need to win to top Group A4, and is considered a major doubt for Barca's LaLiga showdown with Atletico Madrid next Saturday.
The 32-year-old has started all seven of Barca's league games this term and has appeared in all three Champions League matches.
However, Busquets' figures in other areas have dropped since last season, leading to calls for Miralem Pjanic to be given the nod in Ronald Koeman's starting line-up.
Busquets' passes-per-game figures are down from 93 per game last term to 80 this time around, while his number of dribbles (0.83 to 0.48) and touches (106 to 91) have also fallen.
Barca face Atletico and Osasuna in their next two LaLiga games, either side of a trip to Dynamo Kiev in the Champions League.