Wolves beat champions City to win the final following a penalty shootout in China.
“He was top," Guardiola said. “Unfortunately last season we miss him a lot. We did incredibly well without him but we are stronger with him.
“Last season he had no holidays, this team he has had time to rest. Hopefully he can reach his level. He is very positive in his mind. He made an incredible first half, really good."
Guardiola says despite his injury-affected 2018-19 season, De Bruyne's belief has never wavered.
“He's a guy who likes to play football - a huge competitor," Guardiola said. “He never loses confidence in himself.
“For the physical condition and don't get injured, that is the most important thing for him tonight. He is a player who is incredible."