Farrell was the stand-out performer at No.10 for the first four rounds of the RBS 6 Nations but since England's hammering against Wales at the Millennium Stadium in the Grand Slam decider - the Saracen has been struggling for form and fitness.
In the Heineken Cup semi-final against Jonny Wilkinson's Toulon - Farrell very much came out second best, while again he was off colour as Saracens crashed out to Northampton in the Aviva Premiership play-off semi-finals last weekend.
Gatland has already confirmed Farrell will have the first bite of the cherry in a Lions shirt against the Barbarians in Hong Kong on June 1, with Sexton joining up late with the squad as Leinster are involved in the end-of-season RaboDirect PRO12 play-off finals.
But despite the decline in his performances - Gatland admits there are no concerns about Farrell travelling to Australia with the Lions this summer.
"It has been tough for Owen but he tends to respond well to adversity and come back stronger," Gatland said.
"One of the reasons we like him is because he is mentally tough.
"He will react well to any criticism and I am sure he will do well on the tour.
"It is disappointing for Saracens but for us it does help our preparation. As well as the two props (Matt Stevens and Mako Vunipola), it gives us an opportunity to work with Owen for the next couple of weeks."