The 24-year-old lasted 51 minutes of the friendly at Estadio de Gran Canaria before he was replaced by Cesar Azpilicueta.
He then left the stadium on crutches as La Roja's doctors waited for test results to affirm the length of time he would be out for.
Jonny has scored one goal in 12 appearances for Wolves during the newly promoted club's steady start to the Premier League season but now faces a spell on the sidelines ahead of the busy festive period.
A statement from Spain's doctors said: "Jonny has suffered a partial rupture of the internal lateral ligament, with no added injuries.
"At all times the medical services of his club have been kept informed and copies of the tests have been sent.
"We estimate he will be out for 5-6 weeks ".
On loan from Atletico Madrid for the season, the full-back has impressed in the Premier League this term and Wolves reportedly want to make his move permanent.