The 31-year-old, who numbers FA Barclaycard Premiership side, Fulham and Scottish Premier Division oufits, Hibernian and Motherwell, amongst his clubs during an illustrious career, netted for Brentford during a practice game held at Millwall's practice ground this afternoon.
In the sweltering heat both teams agreed to participate in three sessions of 30 minutes.
Lehnmann's goal clinched the first game in Brentford's favour, whilst a strike from unsettled winger, Stephen Hunt, gave Wally Downes' men a second victory of the afternoon.
Millwall took the third game 2-0.
The only notable absentee from the squad was Eddie Hutchinson, who missed out through injury.