Rooney has contested his suspension for using offensive, insulting and/or abusive language and his first appearance since being charged is a Champions League clash with the Blues on Wednesday.
Lampard admits there is never a good time to face his England team-mate but feels Rooney could be ready to take his frustrations out on Chelsea.
"Wayne is always a very competitive player and there is never a good time to be playing against him," Lampard said. "But there's a chance that the ban might spur him on even more. When you get negative headlines like he's had it can make you more of a threat.
"It's not for me to say if I was surprised by the charge. The FA have made their decision and I think United have accepted it. But Wayne is a fantastic player and he'll definitely be a threat against us."
Lampard has also said that Chelsea owner Roman Abramovich has not put the players under any undue pressure to win the Champions League, despite the Russian's burning desire to claim the trophy.
The closest Chelsea have come to doing so was in Abramovich's home country in 2008, when only a missed penalty from John Terry prevented them from beating Wednesday's opponents in the final in Moscow.
"I'm sure the owner would be very pleased for us to win it," Lampard said. "But at the same time, he doesn't come in every day and knock our door down, saying, 'Why have I not won this yet? He understands it's the most difficult competition in football.
"I think we've given him some very good times and I know the owner has appreciated it from how he's enjoyed them with us when we've won titles and with the cups. But the Champions League's a huge thing. You want to be known as the best team in Europe by having that trophy."