Chelsea, who were crowned league champions last season, finished two places above Arsenal with a gap of 12 points.
It is no secret that the two bosses don't have the best of relationships and have frequently found themselves exchanging words from either dugout.
"I believe they [Arsenal] have a top manager, I'm not making fun here," Mourinho told BT Sport via the Mirror.
"They will be even harder to beat next season."
A rare act of kindness from the Portuguese manager but blatant honesty which has to be admired. His unsavoury relationship with Wenger reached boiling point last year when he branded the Arsenal manager "a specialist in failure," which many regarded as a disrespectful comment.
It was clearly mind games, though. Something only top managers can get away with like Sir Alex Ferguson, who mastered it against an array of rival managers.
Mourinho and Wenger have previously had bust-ups on the sidelines such as the spat when Wenger confronted the Chelsea boss after he took exception to a challenge made by Gary Cahill.
The French manager pushed Mourinho before the pair were separated by fourth official Jon Moss. Wenger later apologised for his actions.