The Manchester United frontman had been forced to sit out the early days of his latest spell on international duty with the Red Devils but on Tuesday, the 24-year-old returned to net against Cyprus after being introduced from the bench.
The goal took Lukaku's tally for club and country this season to 16, and Vertonghen has warned that his Belgium teammate is ready to take on Liverpool on Saturday lunchtime.
Vertonghen is quoted by The Mirror as saying: "The goal he got against Cyprus was so typical, a ball in behind and he brushed defenders off and smashed the ball into the net. I am sure he will be fine for Manchester United at the weekend.
"He used the first week with us to get fit. He was injured, I spoke to him and his ankle wasn't in good shape but he has used the time well to recover and he is back and fit again."
Lukaku has scored 11 goals in 10 appearances for United in all competitions this season.